IPv6 frag: avoid overflow while parsing extension headers
IPv6 frag: avoid overflow while parsing extension headers

A malicious packet could advertise an extension header length bigger than
the actual packet length, which would cause an overflow.

Change-Id: I277123e6fde6937b0170f2b2e33846bd22848ac4
Signed-off-by: Yoann Desmouceaux <3d2a91419ec85d2544c543fe75d33c8b8dcc5f8e@cisco.com>

milanlenco/vpp,chrisy/vpp,GabrielGanne/vpp-flowtable,muharif/vpp,chrisy/vpp,FDio/vpp,muharif/vpp,GabrielGanne/vpp-flowtable,FDio/vpp,vpp-dev/vpp,chrisy/vpp,GabrielGanne/vpp-flowtable,vpp-dev/vpp,milanlenco/vpp,muharif/vpp,chrisy/vpp,vpp-dev/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,FDio/vpp,muharif/vpp,GabrielGanne/vpp-flowtable,chrisy/vpp,GabrielGanne/vpp-flowtable,vpp-dev/vpp,milanlenco/vpp,milanlenco/vpp,muharif/vpp,FDio/vpp,chrisy/vpp,milanlenco/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,GabrielGanne/vpp-flowtable,vpp-dev/vpp,muharif/vpp,FDio/vpp,milanlenco/vpp,FDio/vpp