shill: IP Address less than operator.

This change introduces a less than operator for both ByteString and IPAddress.
The ByteString less than operator is based on the static IsLessThan method.
IPAddress uses the ByteString less than operator to implement its own.

The IPAddress less than operator is to allow binary searching of IP address
with some of the C++ standard library containers.

TEST=unittest
BUG=chromium:863260

Change-Id: I8a689d12d16440c0744e882bef0186b490fa5bb8
Reviewed-on: https://chromium-review.googlesource.com/1162973
Commit-Ready: Alex Dale <sigquit@google.com>
Tested-by: Alex Dale <sigquit@google.com>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>