Minor LinuxKPI code cleanup:

Minor LinuxKPI code cleanup:
- Declare some static functions in linux_compat.c instead if inside
  various header files.
- Prefix FreeBSD local functions in the LinuxKPI with "linux_" to
  avoid symbol name conflicts in the future and to make debugging
  easier.
- Make the "struct kobj_ktype" declaractions constant to shave off a
  few bytes from the data segment.

MFC after:	1 week
Sponsored by:	Mellanox Technologies