Declare and Implement generic ICMPv6 handler management
Replace old switch-based ICMPv6 type/code management
Register generic handlers for ICMPv6 Echo Request / Reply
Register generic ICMPv6 handlers for IPv6 ND
Register generic ICMPv6 handlers for RPL
Register generic ICMPv6 handlers for ROLL TM
Merge pull request #585 from g-oikonomou/generic-icmp6-in-hooks

Generic ICMPv6 input hooks