sock: add net to prot->enter_memory_pressure callback

The tcp_enter_memory_pressure calls NET_INC_STATS, but doesn't
have where to get the net from.

I decided to add a sk argument, not the net itself, only to factor
all the required sock_net(sk) calls inside the enter_memory_pressure 
callback itself.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/sock.c b/net/core/sock.c
index 2c0ba52..10a64d5 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1442,7 +1442,7 @@
 	/* Under pressure. */
 	if (allocated > prot->sysctl_mem[1])
 		if (prot->enter_memory_pressure)
-			prot->enter_memory_pressure();
+			prot->enter_memory_pressure(sk);
 
 	/* Over hard limit. */
 	if (allocated > prot->sysctl_mem[2])