Revert "rtnl: Add support for netdev event to link messages"

This reverts commit def12888

.

As per discussion between Roopa Prabhu and David Ahern, it is
advisable that we instead have the code collect the setlink triggered
events into a bitmask emitted in the IFLA_EVENT netlink attribute.

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