nfp: resync repr state when port table sync

If the NSP port table has been refreshed, resync the representor state
with the new port information. At the moment, this only entails looking
for invalid ports and killing off representors associated with them.

The repr instance becomes NULL which is safe since the app accessor
function for reprs returns NULL when it cannot access a repr.

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>