MFC r358996 (by pkelsey):
Fix iflib zero-length fragment handling

MFC r358997 (by pkelsey):
Remove freelist contiguous-indexes assertion from rxd_frag_to_sd()

MFC r358998 (by pkelsey):
Allow iflib drivers to specify the buffer size used for each receive queue

MFC r358999 (by pkelsey):
Remove refill budget from iflib

MFC r359000 (by pkelsey):
Fix if_vmx receive checksum offload bug and harden against the device
skipping receive descriptors

MFC r359001 (by pkelsey):
Adjust if_vmx default receive parameters for better out-of-box performance

MFC r359002 (by pkelsey):
Remove extraneous code from iflib

MFC r359029 (by pkelsey):
Restore power-of-2 queue count constraint from r290948

Tested by: marcus, mav