nfp: add get/set link settings ndos to representors

Since it is now safe to modify link settings for representors, we can
attach the get/set link settings ndos to it. The get/set link settings
are nfp_port based operations.

If a port becomes invalid, the representor will be removed in the same
way a vnic would be.

Signed-off-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>