sparc64: wire up accept4()

This adds the sparc syscall hookups.

Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>