cloudflared_udp_total_sessions was incorrectly a gauge when it
represents the total since the cloudflared process started and will
only ever increase.
Additionally adds new ICMP metrics for requests and replies.
Remove send and return methods from Funnel interface. Users of Funnel can provide their own send and return methods without wrapper to comply with the interface.
Move packet router to ingress package to avoid circular dependency
A funnel is an abstraction for 1 source to many destinations.
As part of this refactoring, shared logic between Darwin and Linux are moved into icmp_posix
Devin Carr
chungthuang