Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Clean up -Wheader-guard warnings.

Submitted by: <dt71@gmx.com>
MFC after: 3 days
X-MFC with: r251848

Add in support for multicast.

Submitted by: Sriram Rapuru at @ Wipro for Exar Inc.
MFC after: 2 weeks

Exar driver for X3100 10GbE Server/Storage adapters

Features: Jumbo frames (up to 9600), LRO (Large Receive Offload),
TSO (TCP segmentation offload), RTH (Receive Traffic Hash).

Submitted by: Sriram Rapuru at Exar
MFC after: 2 weeks