lib: simplify handling of the sysrepo startup configuration

lib: simplify handling of the sysrepo startup configuration

In the new Sysrepo, all SR_EV_ENABLED notifications are followed by
SR_EV_DONE notifications (assuming no errors occur), so there's no
need to special case the SR_EV_ENABLED event anymore (e.g. do full
transactions in one step).

While here, add a few more guarded debug messages to facilitate
troubleshooting.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>