cxgb4: rework TC filter rule insertion across regions

Chelsio NICs have 3 filter regions, in following order of priority:
1. High Priority (HPFILTER) region (Highest Priority).
2. HASH region.
3. Normal FILTER region (Lowest Priority).

Currently, there's a 1-to-1 mapping between the prio value passed
by TC and the filter region index. However, it's possible to have
multiple TC rules with the same prio value. In this case, if a region
is exhausted, no attempt is made to try inserting the rule in the
next available region.

So, rework and remove the 1-to-1 mapping. Instead, dynamically select
the region to insert the filter rule, as long as the new rule's prio
value doesn't conflict with existing rules across all the 3 regions.

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