cxgb4: Re-work the logic for mps refcounting

Remove existing mps refcounting code which was
added only for encap filters and add necessary
data structures/functions to support mps reference
counting for all the mac filters. Also add wrapper
functions for allocating and freeing encap mac
filters.

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