perf trace: Beautify send/recv syscall 'flags' arg

 [root@sandy ~]# perf trace -a -e recvmmsg,recvmsg,recvfrom,sendto,sendmsg,sendmmsg
  6.901 (0.002 ms): 589 recvmsg(fd: 51, msg: 0x7fff35673420, flags: CMSG_CLOEXEC) = -1 EAGAIN Resource temporarily unavailable
  6.966 (0.008 ms): 589 sendmsg(fd: 50, msg: 0x7fff35673230, flags: NOSIGNAL    ) = 961
  6.984 (0.004 ms): 979 sendmsg(fd: 3, msg: 0x7fff5b484940, flags: NOSIGNAL     ) = 945

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-h25k5k50nac0ej5cl5iwgvae@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>