1. Introduced a new subnet extension attribute for this.
When its enabled, this subnet can't be connected to a router.
And to make things simple, this new attribute's value can't
be changed after creation.
2. VM port's active_active_aap mode in the EP file is dtermined
by checking this port's fixded_ip subnets one by one, and only
if the active_active_aap value is true for all the subnets then
we will mark it accordingly in this VM port's EP file. And when
active_active_aap is on, the owned address concept doesn't apply
to those AAPs.
3. An AAP can't be added to a port if this port's
active_active_aap mode is different than any of the other ports
(in the same VRF) whose AAPs is overlapping with this AAP.
4. Also added a helper function to create a subnet with those
extension attributes in the UT environment.
Change-Id: Icb3af7b33442eda739f93f9e6ca16174a26f5c21
(cherry picked from commit 88d3f0ab2a)
(cherry picked from commit 88ac1f4aa6)
(cherry picked from commit 543da14e2841783a1a7b850004a20265e9a0be8d)
(cherry picked from commit 6423c820c4)
01ee7ecedb