Ticket: CM-7756
Reviewed By: roopa
Testing Done: built powerpc and tested ifupdown2 as well as new tests
Once mstpctl-portbpdufilter or mstpctl-bpduguard is enabled for
an interface, removing the configuration in /etc/network/interfaces
does not toggle the mstpctl state back to no.
The root cause of this problem is that "ifreload" does not check default settings for MSTP configuration
for bridge ports and use a default when that setting is removed from the configuration.
This patch adds a check in the existing loop on attribute values.
If there is no configured value, we check to see if a default exists.
self._modinfo['attrs'][attrname]['default'] exists.
If it exists and it is different then the currently running value
we reset the attribute to its default. This is what a customer would expect if
they removed a configured value.
(also added test in cl-tests to check this functionality)
(cherry picked from commit 63d0f7082d44fedabe002aebbb658751dc655a46)
