musl-libc fixed inconsistency between posix and kernl msghdr structures
by adding pad-s.

It initializes all pad-s before calling recvmsg and sendmsg syscalls.
CRIU calls raw system calls from pie code, so we need to intialize pads too.

In addition, we don't initialize msg_flags and iov_len.

https://github.com/xemul/criu/issues/276

https://travis-ci.org/kolyshkin/criu/builds/198415449Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>