MFC r268633, r271046:

Fixes and enhancements for the if_cgem driver...

- miibus fixes as suggested by Yonghyeon Pyun.
- enable VLAN MTU support.
- fix a few WITNESS complaints in cgem_attach().
- have cgem_attach() properly init the ifnet struct before calling
mii_attach() to fix panic when using e1000phy.
- fix ethernet address changing.
- fix transmit queue overflow handling.
- tweak receive queue handling to reduce receive overflows.
- bring out MAC statistic counters to sysctls.
- add e1000phy to config file.
- implement receive hang work-around described in reference guide.
- change device name from if_cgem to cgem to be consistent with other
interfaces.

Fix the Zedboard/Zynq ethernet driver to handle media speed changes so
that it can connect to switches at speeds other than 1gb.

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

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

Bring copyright changes with the agreement of Thomas Skibo.

Communication on src-commiters, Sat, 27 Apr 2013 22:09:06 -0700,
Subject was: "Re: svn commit: r249997"

As I'm here, fix the style main block comments in files' headers.

Add Xilinx Zynq ARM/FPGA SoC support to FreeBSD/arm port.

Submitted by: Thomas Skibo <ThomasSkibo (at) sbcglobal.net>
Reviewed by: wkoszek, freebsd-arm@ (no objections raised)