MFC r352910 and r352911

MFC r352910: iflib: Remove redundant VLAN events deregistration
MFC r352911: ix/ixv: Read MSI-X bar from device config

These fix an issue with a kernel panic on unload with an iflib-using
driver and allow certain HP-branded Intel 10G cards to use MSI-X,
respectively.

Approved by: re@ (gjb@)
Sponsored by: Intel Corporation