BACKPORT: net/compat.c,linux/filter.h: share compat_sock_fprog

BACKPORT: net/compat.c,linux/filter.h: share compat_sock_fprog

Any other users of bpf_*_filter that take a struct sock_fprog from
userspace will need to be able to also accept a compat_sock_fprog
if the arch supports compat calls.  This change allows the existing
compat_sock_fprog be shared.

Signed-off-by: Will Drewry <wad@chromium.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Eric Paris <eparis@redhat.com>
Change-Id: I687cf3c371fdde619db076a46c13b69065e694d4
v18: tasered by the apostrophe police
v14: rebase/nochanges
v13: rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc
v12: rebase on to linux-next
v11: introduction

BUG=chromium-os:27878
TEST=none. Part of a much larger stack that really should merge together.

Change-Id: I8935e627c4152f28856c069e966fd236a74bcd92
Reviewed-on: https://gerrit.chromium.org/gerrit/21359
Reviewed-by: Will Drewry <wad@chromium.org>
Tested-by: Will Drewry <wad@chromium.org>