target/cxgbit: Use T6 specific macro to set the force bit

For T6 adapters use T6 specific macro to set the force bit.

Signed-off-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>