MFC r277396, r278681, r278865, r278924, r279205, r280208,

MFC r277396, r278681, r278865, r278924, r279205, r280208,
  r280210, r280764 and r280768:

Update the Linux compatibility layer:
- Add more functions.
- Add some missing includes which are needed when the header files
  are not included in a particular order.
- The kasprintf() function cannot be inlined due to using a variable
  number of arguments. Move it to a C-file.
- Fix problems about 32-bit ticks wraparound and unsigned long
  conversion. Jiffies or ticks in FreeBSD have integer type and are
  not long.
- Add missing "order_base_2()" macro.
- Fix BUILD_BUG_ON() macro.
- Declare a missing symbol which is needed when compiling without -O2
- Clean up header file inclusions in the linux/completion.h, linux/in.h
  and linux/fs.h header files.

Sponsored by:	Mellanox Technologies

git-svn-id: svn://svn.freebsd.org/base/stable/9@282514 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f