Don't open route socket if we don't need it

Don't open route socket if we don't need it

When automatic-interface-scan is disabled, the route socket was still
being opened.  Add new API to connect / disconnect from the route socket
only as needed.

Additionally, move the block that disables periodic interface rescans to
a place where it actually have access to the configuration values.
Previously, the values were being checked before the configuration was
loaded.

(cherry picked from commit b26079fdaff782ee5d43639d7caa99f1e2c37399)