net: fix compilation with !CONFIG_NET

Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Glauber Costa <glommer@parallels.com>
CC: Hiroyouki Kamezawa <kamezawa.hiroyu@jp.fujitsu.com>
CC: David S. Miller <davem@davemloft.net>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -66,8 +66,20 @@
 
 struct cgroup;
 struct cgroup_subsys;
+#ifdef CONFIG_NET
 int mem_cgroup_sockets_init(struct cgroup *cgrp, struct cgroup_subsys *ss);
 void mem_cgroup_sockets_destroy(struct cgroup *cgrp, struct cgroup_subsys *ss);
+#else
+static inline
+int mem_cgroup_sockets_init(struct cgroup *cgrp, struct cgroup_subsys *ss)
+{
+	return 0;
+}
+static inline
+void mem_cgroup_sockets_destroy(struct cgroup *cgrp, struct cgroup_subsys *ss)
+{
+}
+#endif
 /*
  * This structure really needs to be cleaned up.
  * Most of it is for TCP, and not used by any of