ip4: rework rewrite node to use vlib_buffer_enqueue_to_next()
ip4: rework rewrite node to use vlib_buffer_enqueue_to_next()

- perf improvement is around 3 clock per packet
- it properly prefetches ip header and rewrite area

Credits to zhiyong.yang@intel.com for spotting that in some cases
rewrite area is not prefetched.

Change-Id: Ie02913de7bd7f42b7df2617fb5fa87c74ab53c23
Signed-off-by: Damjan Marion <9141bba8b2efed526e55cf796d48631af330ad98@cisco.com>

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