People familiar with LISP are used to the concept of a mapping cache in
a LISP Tunnel Router. Explain how that concept maps to OVS flow rules.
Additionally, mention that eth0 need not be added in all example
scenarios.
Signed-off-by: Lorand Jakab <lojakab@cisco.com> Signed-off-by: Ben Pfaff <blp@nicira.com>