security: struct security_operations kerneldoc fix

unix_may_send hook has the prototype:

int (*unix_may_send) (struct socket *sock, struct socket *other)

so the documentation is wrongly referring to the second argument as @sock.

Signed-off-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>