Update the mlx4 core and mlx4en(4) modules towards Linux v4.9.

Background:
The coming ibcore update forces an update of mlx4ib(4) which in turn requires
an updated mlx4 core module. This also affects the mlx4en(4) module because
commonly used APIs are updated. This commit is a middle step updating the
mlx4 modules towards the new ibcore.

This change contains no major new features.

Changes in mlx4:
a) Improved error handling when mlx4 PCI devices are
detached inside VMs.
b) Major update of codebase towards Linux 4.9.

Changes in mlx4ib(4):
a) Minimal changes needed in order to compile using the
updated mlx4 core APIs.

Changes in mlx4en(4):
a) Update flow steering code in mlx4en to use new APIs for
registering MAC addresses and IP addresses.
b) Update all statistics counters to be 64-bit.
c) Minimal changes needed in order to compile using the
updated mlx4 core APIs.

Sponsored by: Mellanox Technologies
MFC after: 1 week

Move the ConnectX-3 and ConnectX-2 driver from sys/ofed into sys/dev/mlx4
like other PCI network drivers. The sys/ofed directory is now mainly
reserved for generic infiniband code, with exception of the mthca driver.

- Add new manual page, mlx4en(4), describing how to configure and load
mlx4en.

- All relevant driver C-files are now prefixed mlx4, mlx4_en and
mlx4_ib respectivly to avoid object filename collisions when compiling
the kernel. This also fixes an issue with proper dependency file
generation for the C-files in question.

- Device mlxen is now device mlx4en and depends on device mlx4, see
mlx4en(4). Only the network device name remains unchanged.

- The mlx4 and mlx4en modules are now built by default on i386 and
amd64 targets. Only building the mlx4ib module depends on
WITH_OFED=YES .

Sponsored by: Mellanox Technologies