allow to load kernel modules from vendor partition

The kernel  modules under /vendor partition has been relabeled to vendor_file.
This CL allows for the modprobe to load modules labeled vendor_file.

Kernel modules are loaded in init.rc with following commands:
    exec u:r:modprobe:s0 -- /system/bin/modprobe -d /vendor/lib/modules MODULE

Bug: 35653245
Test: tested on sailfish
Change-Id: I2132ca4de01c5c60476dad8496e98266de5a1bb7