tcp: export tcp_enter_cwr()

Upcoming tcp_cdg uses tcp_enter_cwr() to initiate PRR. Export this
function so that CDG can be compiled as a module.

Cc: Eric Dumazet <[email protected]>
Cc: Yuchung Cheng <[email protected]>
Cc: Stephen Hemminger <[email protected]>
Cc: Neal Cardwell <[email protected]>
Cc: David Hayes <[email protected]>
Cc: Andreas Petlund <[email protected]>
Cc: Dave Taht <[email protected]>
Cc: Nicolas Kuhn <[email protected]>
Signed-off-by: Kenneth Klette Jonassen <[email protected]>
Acked-by: Yuchung Cheng <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

net/ipv4/tcp_input.c

@@ -2552,6 +2552,7 @@ void tcp_enter_cwr(struct sock *sk)
 		tcp_set_ca_state(sk, TCP_CA_CWR);
 	}
 }
+EXPORT_SYMBOL(tcp_enter_cwr);
 
 static void tcp_try_keep_open(struct sock *sk)
 {