inetpeer: Add redirect and PMTU discovery cached info.

Validity of the cached PMTU information is indicated by it's
expiration value being non-zero, just as per dst->expires.

The scheme we will use is that we will remember the pre-ICMP value
held in the metrics or route entry, and then at expiration time
we will restore that value.

In this way PMTU expiration does not kill off the cached route as is
done currently.

Redirect information is permanent, or at least until another redirect
is received.

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inetpeer.h

@@ -50,6 +50,10 @@ struct inet_peer {
 			u32				metrics[RTAX_MAX];
 			u32				rate_tokens;	/* rate limiting for ICMP */
 			unsigned long			rate_last;
+			unsigned long			pmtu_expires;
+			u32				pmtu_orig;
+			u32				pmtu_learned;
+			struct inetpeer_addr_base	redirect_learned;
 		};
 		struct rcu_head         rcu;
 	};

net/ipv4/inetpeer.c

@@ -515,6 +515,8 @@ struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
 		p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
 		p->rate_tokens = 0;
 		p->rate_last = 0;
+		p->pmtu_expires = 0;
+		memset(&p->redirect_learned, 0, sizeof(p->redirect_learned));
 		INIT_LIST_HEAD(&p->unused);