vxlan: changelink: Inline vxlan_dev_configure()

The changelink operation may cause change in remote address, and
therefore an FDB update, which can be vetoed. To properly handle
vetoing, vxlan_changelink() needs to be gradually updated.

In this patch simply replace vxlan_dev_configure() with the two
constituent calls.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>