MFC r256694, r256713, r256714.

r256694:
iw_cxgbe: iWARP driver for Chelsio T4/T5 chips. This is a straight port
of the iw_cxgb4 found in OFED distributions.

r256713:
iw_cxgbe should have a dependency on t4nex.

r256714:
Fix typo in previous commit.

Approved by: re (hrs)