lib: correctly exit CLI nodes on file config load

lib: correctly exit CLI nodes on file config load

The (legacy) code for reading split configs tries to execute config
commands in parent nodes, but doesn't call the node_exit function when
it goes up to a parent node.  This breaks BGP RPKI setup (and extended
syslog, which is in the next commit.)

Doing this correctly is a slight bit involved since the node_exit
callbacks should only be called if the command is actually executed on a
parent node.

Signed-off-by: David Lamparter <equinox@diac24.net>