net: fix compat_sys_recvmmsg parameter type

compat_sys_recvmmsg has a compat_timespec parameter and not a
timespec parameter. This way we also get rid of an odd cast.

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>