MFC 292736:
cxgbe(4): Updates to the base NIC driver and t4_tom to support the iSCSI
offload driver. These changes come from projects/cxl_iscsi.

Note that these changes make use of the mbufq API from 11.0, but that
API is not present in 10.x in the same form. Borrow an implementation
from the CAM CTL ha code that uses m_nextpkt to implement mbufq for use
in 10.