BB: ubox: kmodloader: support loading kmods from multiple directories

BB: ubox: kmodloader: support loading kmods from multiple directories

This is required during early boot in the extroot setup phase to support
loading kmods from the overlay that depend on kmods on the rom partition.

The subsequent mount_root updates will use the LD_LIBRARY_PATH env
variable to pass kmod directories to kmodloader.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
Backport of r42813, r44533

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@44536 3c298f89-4303-0410-b956-a3cf2f4a3e73