Use a ticker to setup an alarm and the matching alarm handler. It
removes the need to used shared variables and signal states.

Initialize and use the fd sets correctly when using select().

The loops are now interrupted using the self-pipe trick. It allows to
receive signals and reduce the processing done in the handler to a
minimum without introducing races.

Adds a ticker package to manipulate the set timer/alarm signals more
easily. The implementation of the package tries to maintain a consistent
state of the system before and after use.

Refactors the code to avoid using "exit()" outside main() functions. The
changeset also changes the flow to avoid relying on functions side
effects.

Ensure warnings will be treated as errors by the compiler, it required a
fix to remove unused function from the code generated by flex.

The CL gets rid of old style function prototypes like:
    int main(argc, argv)
    int argc;
    char *argv[];
    {
     ...
    }
because it is not supported by any C standard anymore and will not
compile in the future.

This CL leverages the style of the source code by providing a clang-format
configuration for the project. All the files have been formatted with the new
style. A gitignore file was added to avoid checking in build products.

To format your files: clang-format --style=file -i <filename>

Usage was wrong, use default macros.
Typos, language and some indent fixes.

On BSD/MacOS the list of syscall considered as reentrant or not interruptible
by signals and signal-safe is limited. Calling any other function from a signal
handler may lead to undefined behavior. Before this CL, the signal handler was
in charge of printing the histogram and a summary of the session.

The receive loop and the handler are now using a pipe to transmit the 'exit'
message. On one hand loop uses select to listen on the pipe read end and the
UDP socket, when the pipe unblocks the select, the loop knows it has to leave.
On the other end the handler just closes the write end of the pipe (as close()
is allowed in signal handlers).

Bonus: there's no need to keep the histogram state as global variables.

Sometimes some data is missing when interrupting commands. Flush outputs
before leaving.

Sometimes the magic packet is dropped when sending in flood mode on
Linux. Let the stack recover before sending so that the packet makes it
through.

More precisions on -o in udptarget usage message.

Add second TARGET example.

Do not fill buffer and zero out last character after strncpy.
Type parameters instead of relying on default int type.
Homogenize error reporting for getaddrinfo.

The port to the registry is now open, use docker images stored in the
project

Dockerfile to build the required image. Note that there is a specific
runner launched with the --sysctl net.ipv6.conf.all.disable_ipv6=0
docker option to enable IPv6 that is disabled by default.
Also remove the trap SIGSEGV in one test, it seems useless and crashes
inside docker with: trap: SIGSEGV: bad trap

When the backlog is zero on a Linux kernel without syn_cookies present
or enabled (check /proc/sys/net/ipv4/tcp_syncookies), connections will
fail with a log like
TCP     : request_sock_TCP: Possible SYN flooding on port 13000. Dropping request.  Check SNMP counters.

The default compiler on FreeBSD is set by default with -fno-common,
triggering loads of multiple definition errors at link time.
This is a temporary fix, we should instead force no-common and fix code
accordingly.

Triggers loads of macro redefined warnings

Android cross-compilation environment
Android ndk: android-ndk-r16b
Compiler: arm-linux-androideabi-clang

IPMT modifications
tcptarget.c, udptarget.c: Change old index(...) call to strchr(...)
tcpmt.c: Change getdtablesize() call to sysconf(_SC_OPEN_MAX)

Change to more understandable names
c to cycle
s to sock
sa to passive_sock

Stdout was not flushed which caused a problem when not using a
TTY, output was buffered and displayed all at once at the end of
a session.

Testing: check that the stats are printed every second when
running udpmt -Vr 10 localhost | less

message d'avertissement si c'est le cas.
udptarget : si la longueur de paquet reçue est inférieure à 4, affiche un
message et désactive le traitement des numéros de séquence.

Contrib. by Baptiste Jonglez : setting msg.msg_namelen to the right size, to support both IPv4 and IPv6.