proxy_arp: remove unused is_add
proxy_arp: remove unused is_add

Change-Id: I1773d962b373693a737d39c0c97e8c53eb91545a
Signed-off-by: Marek Gradzki <3ca09cd7b7147613247c2a96dcdb0ba33114f8e7@cisco.com>

chrisy/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,vpp-dev/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,FDio/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp