Add ICMP type/code and udplite/sctp in Nettrace.

This adds support for additional protocols and also provides more clear
semantics of protocol specific fields, such as only including tcpFlags
when the protocol is IPPROTO_TCP.

Test: atest libnetworkstats_test & flash and trace
Change-Id: Ic69fc75e85ebf8734027c942a253af4972ad14d8