cxgb4: add TC-MATCHALL classifier ingress offload

Add TC-MATCHALL classifier ingress offload support. The same actions
supported by existing TC-FLOWER offload can be applied to all incoming
traffic on the underlying interface.

Ensure the rule priority doesn't conflict with existing rules in the
TCAM. Only 1 ingress matchall rule can be active at a time on the
underlying interface.

v5:
- No change.

v4:
- Added check to ensure the matchall rule's prio doesn't conflict with
  other rules in TCAM.
- Added logic to fill default mask for VIID, if none has been
  provided, to prevent conflict with duplicate VIID rules.
- Used existing variables in private structure to fill VIID info,
  instead of extracting the info manually.

v3:
- No change.

v2:
- Removed logic to fetch free index from end of TCAM. Must maintain
  same ordering as in kernel.

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