zebra: dup addr detect clear cmd non-zero return

zebra: dup addr detect clear cmd non-zero return

Clear dup address vni needs to return non-zero value
in case of command is not successful.

Ticket:CM-23122
Testing Done:
run clear command and check upon failure return code is non-zero.

root@TORS1:~# vtysh -c "clear evpn dup-addr vni 1000 ip 45.0.1.26"
% Requested IP's associated MAC 00:01:02:03:04:05 is still in duplicate
% state
root@TORS1:~# echo $?
1

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