cxgb4: Assign filter server TIDs properly

The LE workaround code is incorrectly reusing the TCAM TIDs
(meant for allocation by firmware in case of hash collisions) for filter
servers. This patch assigns the filter server TIDs properly starting from
sftid_base index.

Based on original work by Santosh Rastapur <santosh@chelsio.com>

Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>