net/sock.h: fix sk_peek_off kernel-doc warning

Fix kernel-doc warning in net/sock.h:

Warning(include/net/sock.h:377): No description found for parameter 'sk_peek_off'
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -246,6 +246,7 @@ struct cg_proto;
   *	@sk_user_data: RPC layer private data
   *	@sk_sndmsg_page: cached page for sendmsg
   *	@sk_sndmsg_off: cached offset for sendmsg
+  *	@sk_peek_off: current peek_offset value
   *	@sk_send_head: front of stuff to transmit
   *	@sk_security: used by security modules
   *	@sk_mark: generic packet mark