Change dnsmasq input command argument separator

Heretofore netd issued commands to dnsmasq over a stdin channel
using ":" as an argument separator. This make it very complicated
to issue commands that involve IPv6 addresses.

This changes the separator from ":" to "|".

Additionally:

    - Pass DHCP range string literals through to startTethering(),
      still performing string literal to IPv4 address validation.

Bug: 9580643
Change-Id: I210daf311a4c3d84dae3ed054b92c9fa399a791f