ospfd: Restoring the original tag in external lsas

ospfd: Restoring the original tag in external lsas

Description:
When a routemap applied to set a tag, all the permitted routes are
refreshed with new tag, but when a different route map applied with
a different action still the same tag persits in the external route.
The actual tag received from zebra is expected to be set back to the
routes here. Corrected this behaviour by restoring a original tag
received from zebra.

Signed-off-by: Rajesh Girada <rgirada@vmware.com>