DHCPv6 Proxy; fix crash when DHCPv6 prxy is not configured and client packet is received
DHCPv6 Proxy; fix crash when DHCPv6 prxy is not configured and client packet is received

Change-Id: I0250acdee803545b8923549e2099863a95544691
Signed-off-by: Neale Ranns <7d187a79c6b4bf1b7a865a4d130ff0038bf5d84b@cisco.com>

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