MFC r316541, r316544, and r320688 from HEAD to stable/11.

r316541:
Fix a double free in ixgbe_rxeof()

r316544:
Don't overwrite vf->flags variable at the end of ixgbe(4) ixgbe_add_vf()

r320688:
ixgbe(4): Update HEAD (p3) to 3.2.12-k

Includes:

• Support for X550EM devices.
• Support for Bypass adapters.
• Flow Director code moved to separate files
• SR-IOV code moved to separate files
• Netmap code moved to separate files

Sponsored by: Intel Corporation