Only validate local_ip if using tunneling

Only validate local_ip if using tunneling

Change I4b4527c28d0738890e33b343c9e17941e780bc24 introduced a new
validation to make sure that local_ip holds a valid IP that is present
in one of the interfaces on the machine. However, this test is not
relevant if tunneling is not enabled, since the value is ignored anyway.

This patch changes validate_local_ip to not check local_ip in case
tunneling is not enabled (if no value was put in the 'tunnel_types'
option).

Change-Id: I07119341076573a4226b5ad998bdff09c021ae30
Closes-Bug: #1487053
Related-Bug: #1408603