inet: Minimize use of cached route inetpeer.

Only use it in the absolutely required cases:

1) COW'ing metrics

2) ipv4 PMTU

3) ipv4 redirects

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

diff --cc net/ipv4/icmp.c
Simple merge

diff --cc net/ipv4/route.c
Simple merge

diff --cc net/ipv6/icmp.c
Simple merge

diff --cc net/ipv6/ip6_output.c
Simple merge

diff --cc net/ipv6/ndisc.c
Simple merge