Fix for bug https://bugs.launchpad.net/juniperopenstack/+bug/1362774. 1) When the DF bit is set in the packet from VM, vrouter Traps the packet to Agent. Agent expects the packet to be with ethernet header. But Vr_pcow() is removing the ethernet header for multicast packets leading to ICMP error not being generated by Agent. As a fix, vr_pcow() is modified to retain the ethernet header. 2) Removing the vr_palloc_head() from Multi_proto nexthop as this is no more required

Change-Id: I57ab54c81672e20f9e5e3ce275730a5e3875c258