Add support for overlay networking in older kernels.
Following were done to achieve this:
+ Create the vxlan network in host namespace.
+ This may create conflicts with other private
networks so check for conflicts and fail a
join if there is any conflict.
+ Add iptable based filtering to only allow
subnet bridges in the same network to forward
traffic while different network bridges will
not be able to forward b/w each other. Also
block traffic to overlay network originating
from the host itself.
Signed-off-by: Jana Radhakrishnan <mrjana@docker.com>
