Bug #344318 socketcall should wrap recvmmsg and sendmmsg

Some architectures, e.g. s390, don't have dedicated recvmmsg and sendmmsg
system calls, but use the socketcall multiplexing system call with
SYS_RECVMMSG or SYS_SENDMMSG (just like the accept4 systemcall can also
be called through socketcall). Create separate helpers for recvmmsg and
sendmmsg helpers that can be used by either the direct syscall or the
socket call.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14964 a5019735-40e9-0310-863c-91ae7b9d1cf9
4 files changed