Fix for VM deletion issue

Fix for VM deletion issue

Route path entry is getting removed from
FIB table after VM deletion->

If multiple VMs are present in the same CSS and
an extra-route is configured with nexthop being
both such VMs, then if one of the VM is removed,
the entire route-path representing that CSS nexthop
is getting removed from FIB.

Consequence -> If further deletion of VM takes place,
then it won't update the flows and groups.

Fix -> This is fixed by checking if extra-route is present
behind at least one VM, then do not remove or update fib entry
for route-path representing that CSS nexthop, just update
vpntoextraroute and prefixtointerface DS.

Change-Id: I885fd307db4b571e4fa11a1626e3b2a95bf25c89
Signed-off-by: eswanit <swati.udhavrao.niture@ericsson.com>