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.

Remove the call with an empty string in the first place.
bind_source more robust to empty parameters.

Changes the behaviour of the -S option which can take a full source
specification now instead of just a port number. This option now accepts a
value of the form [host][:port] where host can be an address or hostname and
port a numeric value or service name.
Replaces char[] srcportname with char* source and removes strncpy since getopt
optarg is a pointer into the original argv array.