Add missing case for DNS_CONFIG

Found compiling with -Werror
Share Packet checksum values for TCP, UDP, IPv6. ICMPv4 and ICMPv6

Keep a separate checksum for IPV4, since a packet can have both an IPV4
checksum and a TCPV4 checksum, or IPV4 and UDPV4 checksum.

This will allow future sharing of more values.

Use PACKET_RESET_CHECKSUMS() in Unit Tests in place of setting the
individual checksum values.