cxgb4: Reserve stid 0 for T4/T5 adapters

When creating offload server entries, an IPv6 passive connection request
can trigger a reply with a null STID, whereas the driver would expect
the reply 'STID to match the value used for the request.
This happens due to h/w limitation on T4 and T5.

This patch ensures that STID 0 is never used if the stid range starts
from zero.

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>