ipv4: Calling ->cow_metrics() now is a bug.
Nothing every writes to ipv4 metrics any longer. PMTU is stored in rt->rt_pmtu. Dynamic TCP metrics are stored in a special TCP metrics cache, completely outside of the routes. Therefore ->cow_metrics() can simply nothing more than a WARN_ON trigger so we can catch anyone who tries to add new writes to ipv4 route metrics. Signed-off-by: David S. Miller <firstname.lastname@example.org>