cxgbe(4): Fix netmap rx behavior with nm_split_rss

The driver should look for active queues and one potential default-queue
in both halves of the split instead of stopping at the first valid
default-queue.

Fixes: a9f476580eb0 cxgbe(4): fixes for netmap operation with only some queues active
MFC after: 1 week
Sponsored by: Chelsio Communications