ip: fix cancel termination after receive malformed ip6 packet

This fix is for cancel termination of vpp after receive malformed
packet type of ip6.To avoid termination of vpp are checked if are
missing data in packet. This occours, when payload length in ip6
header packet is more than real count of data in packet. When
this error occours, packet is ignore.

Type: fix
Ticket: VPP-1693, VPP-1694

Change-Id: I9d9ecea7b75c8702cb31aa8051c8d4d7ce19659d
Signed-off-by: johny <jan.cavojsky@pantheon.tech>