ip4: don't format upper layer if it's a fragment
ip4: don't format upper layer if it's a fragment

Parsing ipv4 upper layer is not meaningful
if it's a fragment packet except the first.

Change-Id: I442fb7ec01244fde8c4f7656a8ba633d0aa0f97e
Signed-off-by: Faicker Mo <187c775570212e164f9980b8efee7fd87c8e8745@ucloud.cn>

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