cxgb4: insert IPv6 filter rules in next free region

IPv6 filters can occupy up to 4 slots and will exhaust HPFILTER
region much sooner. So, continue searching for free slots in the
HASH or NORMAL filter regions, as long as the rule's priority does
not conflict with existing rules in those regions.

Signed-off-by: Rahul Kundu <rahul.kundu@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>