cxgb4: use firmware API for validating filter spec

Adds support for validating hardware filter spec configured in firmware
before offloading exact match flows.

Use the new fw api FW_PARAM_DEV_FILTER_MODE_MASK to read the filter mode
and mask from firmware. If the api isn't supported, then fall-back to
older way of reading just the mode from indirect register.

Signed-off-by: Raju Rangoju <rajur@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>