[NET]: prot_inuse cleanups and optimizations

1) Cleanups (all functions are prefixed by sock_prot_inuse)

sock_prot_inc_use(prot) -> sock_prot_inuse_add(prot,-1)
sock_prot_dec_use(prot) -> sock_prot_inuse_add(prot,-1)
sock_prot_inuse()       -> sock_prot_inuse_get()

New functions :

sock_prot_inuse_init() and sock_prot_inuse_free() to abstract pcounter use.

2) if CONFIG_PROC_FS=n, we can zap 'inuse' member from "struct proto",
since nobody wants to read the inuse value.

This saves 1372 bytes on i386/SMP and some cpu cycles.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/udp.h b/include/net/udp.h
index 93796be..c6669c0 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -115,7 +115,7 @@
 	write_lock_bh(&udp_hash_lock);
 	if (sk_del_node_init(sk)) {
 		inet_sk(sk)->num = 0;
-		sock_prot_dec_use(sk->sk_prot);
+		sock_prot_inuse_add(sk->sk_prot, -1);
 	}
 	write_unlock_bh(&udp_hash_lock);
 }