zebra: unset sticky mac upon local deletion

zebra: unset sticky mac upon local deletion

if the local sticky mac delete request is received,
if there are associated neighbor entries present, mac's
only local flag is removed and marked as auto mac.

this results in next local mac learning automatically assumes
mac is sticky.

There is a case when bridge learning off is configured, user
configures sticky mac via bridge fdb add.
This MAC learns associated neighbor entry.
Later user deletes stick mac via bridge fdb del, this triggers
frr to delete mac but if there are neighbors present, frr marks
MAC as AUTO but does not remove sticky flag.
User enables bridge learning on which triggers
The mac to learn as dynamic entry and in absence of this
fix, the mac is marked as sticky.

Ticket:CM-24968
Reviewed By:CCR-8683
Testing Done:

Validated broken condition with internally reproduction
with fix and without.

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>