Bug 1915 : Configuration knob for enabling L3 fwd in OVSDB

Bug 1915 : Configuration knob for enabling L3 fwd in OVSDB

OVSDB L3 fwd code will check for system property 'ovsdb.l3.fwd.enabled'
to determine whether it should be enabled upon OVSDB init.

To enable it, all that is needed is something like:
   echo 'ovsdb.l3.fwd.enabled=yes' >> ./configuration/config.ini

To disable, all that is needed is something like:
   sed -i -e 's/ovsdb\.l3\.fwd\.enabled\=.*$/ovsdb\.l3\.fwd\.enabled=no/'  ./configuration/config.ini

Change-Id: Ia00bcc0058b94d23b8497077241c5208ebae2081
Signed-off-by: Flavio Fernandes <ffernand@redhat.com>