MFC r291072, r291168 and r291169:

MFC r291072, r291168 and r291169:
Add the mlx5 and mlx5en modules to the i386 and amd64 kernel builds by
default and add a manual page for mlx5en. The mlx5 module contains
shared code for both infiniband and ethernet. The mlx5en module
contains specific code for ethernet functionality only. A mlx5ib
module is in the works for infiniband support.

Supported hardware:
- ConnectX-4: 10/20/25/40/50/56/100Gb/s speeds.
- ConnectX-4 LX: 10/25/40/50Gb/s speeds (low power consumption)

Refer to the mlx5en(4) manual page for a comprehensive list.

The team porting the mlx5 driver(s) to FreeBSD:
- Hans Petter Selasky <hselasky@freebsd.org>
- Oded Shanoon <odeds@mellanox.com>
- Meny Yossefi <menyy@mellanox.com>
- Shany Michaely <shanim@mellanox.com>
- Shahar Klein <shahark@mellanox.com>
- Daria Genzel <dariaz@mellanox.com>
- Mark Bloch <markb@mellanox.com>

Differential Revision:	https://reviews.freebsd.org/D4163
Sponsored by:	Mellanox Technologies

git-svn-id: svn://svn.freebsd.org/base/stable/10@291201 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f