Fix (one of) 4.9-RELEASE release breaker, "Loading kernel modules while
installation phase sometimes causes an error" bug. It also includes
"there's an error while loading firewire modules" bug.

Since the results of readdir(3)'s whims, either sbp.ko or if_fwe.ko is
picked up for load BEFORE firewire.ko. Unfortunately module_path is
not properly set, kldload(2) cannot find kernel modules, firewire.ko,
which is required to load sbp.ko/if_fwe.ko. This is why you'll see
"loading failed" message.

Actually these are mostly comes from following commits on the HEAD:
src/release/Makefile rev 1.721
src/usr.sbin/sysinstall/modules.c rev 1.5

Approved by: murray (as of re@, pre-approved)