Explicitly check for existence of the root directory in drv_init
Explicitly check for existence of the root directory in drv_init

Previously a failure would only occur if bridge_physdevs() tried to
access something in the root directory and failed. That function will
no longer be called (see the next commit), so add a stat() of the
provided root and make sure it's a directory.

emaste/netcf,osier/netcf,seanbruno/fbsd-netcf,osier/netcf,emaste/netcf,hallyn/netcf,battlemidget/deprecated-mingw32-netcf,battlemidget/deprecated-mingw32-netcf,seanbruno/fbsd-netcf,osier/netcf,hallyn/netcf,seanbruno/fbsd-netcf,hallyn/netcf,emaste/netcf