MFC r315201, r315920, r315921, r315922, r316008, and r316062.

r315201:
cxgbe(4): Fix an always-true assertion (reported by PVS-Studio).

sys/dev/cxgbe/t4_main.c: PVS-Studio: Expression is Always True (CWE-571) (3)

r315920:
cxgbe/iw_cxgbe: c4iw_connect should always returns a -ve errno on failure.

r315921:

cxgbe/iw_cxgbe: alloc_ep expects a gfp_t, and it's always ok to sleep during
alloc_ep.

r315922:
cxgbe/iw_cxgbe: allocations that use GFP_KERNEL (which is M_WAITOK on
FreeBSD) cannot fail.

r316008:
cxgbe/iw_cxgbe: Remove unused code.

r316062:
cxgbe/iw_cxgbe: Defer the handling of error CQEs and RDMA_TERMINATE to
the thread that deals with socket state changes. This eliminates
various bad races with the ithread.