ipv4: Don't pre-seed hoplimit metric.

Always go through a new ip4_dst_hoplimit() helper, just like ipv6.

This allowed several simplifications:

1) The interim dst_metric_hoplimit() can go as it's no longer
   userd.

2) The sysctl_ip_default_ttl entry no longer needs to use
   ipv4_doint_and_flush, since the sysctl is not cached in
   routing cache metrics any longer.

3) ipv4_doint_and_flush no longer needs to be exported and
   therefore can be marked static.

When ipv4_doint_and_flush_strategy was removed some time ago,
the external declaration in ip.h was mistakenly left around
so kill that off too.

We have to move the sysctl_ip_default_ttl declaration into
ipv4's route cache definition header net/route.h, because
currently net/ip.h (where the declaration lives now) has
a back dependency on net/route.h

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 3b06770..748cb5b 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1430,9 +1430,9 @@
 	return ret;
 }
 
-int ipv4_doint_and_flush(ctl_table *ctl, int write,
-			 void __user *buffer,
-			 size_t *lenp, loff_t *ppos)
+static int ipv4_doint_and_flush(ctl_table *ctl, int write,
+				void __user *buffer,
+				size_t *lenp, loff_t *ppos)
 {
 	int *valp = ctl->data;
 	int val = *valp;