[S390] Ignore sendmmsg system call note wired up warning

sendmmsg is reachable via the socket system call. We don't enable a second
way on s390 to reach the same system call.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>