MFC r329703:
Allow LinuxKPI character devices to receive mmap() calls from the Linux
binary mode user-space emulation layer. This is a regression issue after
r328436, when LinuxKPI character devices started to use DTYPE_DEV in
the "f_type" field of the associated file structure(s).

Found by: Johannes Lundberg <johalun0@gmail.com>
Sponsored by: Mellanox Technologies