Merge branch 'net-metrics-consolidate'

David Ahern says:

====================
net: Consolidate metrics handling for ipv4 and ipv6

As part of the IPv6 fib info refactoring, the intent was to make metrics
handling for ipv6 identical to ipv4. One oversight in ip6_dst_destroy
led to confusion and a couple of incomplete attempts at finding and
fixing the resulting memory leak which was ultimately resolved by
ce7ea4af

 ("ipv6: fix memory leak on dst->_metrics").

Refactor metrics hanlding make the code really identical for v4 and v6,
and add a few test cases.
====================

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