zebra: Double check is not necessary in nexthop_active_update

zebra: Double check is not necessary in nexthop_active_update

The nexthop_active_update command looks at each individual
nexthop and decides if it has changed.  If any nexthop
has changed we will set the re->status to ROUTE_ENTRY_CHANGED
and ROUTE_ENTRY_NEXTHOPS_CHANGED.

Additionally the test for old_nh_num != curr_active
makes no sense because suppose we have several events
we are processing at the same time and a total ecmp
of 16 but 14 are active at the start and 14 are active
at the end but different interfaces are up or down.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>