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