cxgb4: Update SGE context congestion map change for T6 adapter

SGE context congestion map changed from 4 to 8 priority per port
in T6 as there are only 2 channels.

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