zebra: only pass mpls proto type if doing install

zebra: only pass mpls proto type if doing install

Problem reported with not deleting LSPs from the zebra kernal mpls table
when a delete occurred in bgp.  Found that we were exiting the delete
process incorrectly due to not being able to derive the route_type from
the best_nhlre on the lsp while deleting. Since this info was only
needed for route installation, removed this early exit in the case of
deleting the lsp.

Signed-off-by: Don Slice <dslice@cumulusnetworks.com>
Ticket: CM-18309
Reviewed By: CCR-6781
Testing Done:  Manual testing looks good.  mpls tests successful