UPSTREAM: net: socket: Make unnecessarily global sockfs_setattr() static

Make sockfs_setattr() static as it is not used outside of net/socket.c

This fixes the following GCC warning:
net/socket.c:534:5: warning: no previous prototype for ‘sockfs_setattr’ [-Wmissing-prototypes]

Fixes: 86741ec2 ("net: core: Add a UID field to struct sock.")
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Fixes: android-4.9 commitID 81a15910
       ("UPSTREAM: net: core: Add a UID field to struct sock.")
(cherry picked from commit dc647ec8)
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>