provided in the kernel build directory, fix modules that were
failing to build this way due to not quite correct kernel option
usage. In particular:
ng_mppc.c uses two complementary options, both of which are listed
in sys/conf/files. Ideally, there should be a separate option for
including ng_mppc.c in kernel build, but now only
NETGRAPH_MPPC_ENCRYPTION is usable anyway, the other one requires
proprietary files.
nwfs and smbfs were trying to ensure they were built with proper
network components, but the check was rather questionable.
Discussed with: ru