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

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

ixgbe(4): Update to version 3.1.13-k

Add support for two new devices: X552 SFP+ 10 GbE, and the single port
version of X550T.

Submitted by: erj
Reviewed by: gnn
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D4186

Add support for certain Intel X550 devices.

These include standalone X550 adapters, X552 10GbE backplane, and
X552/X557-AT 10GBASE-T; with the latter two being integrated into Xeon D SoCs.

As well, this bumps the ixgbe version number to 2.8.3, and includes updates
to shared code for support for the new devices.

Differential Revision: D2414
Reviewed by: gnn, adrian
Approved by: jfv (mentor), gnn (mentor)