Properly handle empty before/after notifications in l2pop code

Change-Id: I8644bb7cc2afb3b181397a478f96927990c0a4ca
Closes-Bug: #1367881
ofagent: Fix a possible crash in arp responder

Be careful for exceptions when feeding packet-in data,
which is generated by tenant VMs and thus can not be trusted,
to Ryu packet library.

Closes-Bug: #1365255
Change-Id: Ia8bacfb55def563a1b23a47709ae72bd4fce0fce
Remove an argument that is never used

This code was creating a dict with a gw_exists key.  I was curious to
know who was interested in receiving this information down the line.
However, no one is ever interested in that key.  It took me some time
to follow this through wondering what was going on and found only dead
ends.

Change-Id: I755d9628ab750b950b33f5dcf32ccf2a9b00800e
Avoid constructing a RouterInfo object to get namespace name

Constructing a RouterInfo object just for a string concatenation is
inefficient and adds more dependence on the class which needs
refactoring.

Change-Id: Ibaf369d6ebe9285a0c845802def59bfa26ac0fd5
Use EUI64 for IPv6 SLAAC when subnet is specified

This commit uses EUI64 for SLAAC and stateless IPv6 address
when subnet id in fixed_ip is specified.

After this patch, all the ports created on a subnet which has
ipv6_address_mod=slaac or ipv6_address_mod=dhcpv6-stateless
will use EUI64 as the address.
This patch also checks if fixed IP address is specified
for a IPv6 subnet with address mode slaac or dhcpv6-stateless
during creating or updating a port. If yes, raise InvalidInput
error to stop the port creation or update.

Remove unit test test_generated_duplicate_ip_ipv6 because
fixed_ip should not be specified for a slaac subnet.

Change-Id: Ie481cfb2f4313baf44bf1a838ebda374a5c74c6a
Closes-Bug: 1330826
Race for l2pop when ports go up/down on same host

With l2pop enabled, race exists in delete_port_postcommit
when both create/update_port and delete_port deal with
different ports on the same host, where such ports are
either the first (or) last on same network for that host.
This race happens outside the DB locking zones in
the respective methods of ML2 plugin.

To fix this, we have moved determination of
fdb_entries back to delete_port_postcommit and removed
delete_port_precommit altogether from l2pop mechanism
driver.  In order to accomodate dvr interfaces, we
are storing and re-using the mechanism-driver context
which hold dvr-port-binding information while
invoking delete_port_postcommit.  We loop through
dvr interface bindings invoking delete_port_postcommit
similar to delete_port_precommit.

Closes-Bug: #1372438
Change-Id: If0502f57382441fdb4510c81a89794f57a38e696
Merge "Remove an argument that is never used"
Merge "Race for l2pop when ports go up/down on same host"
Merge "ofagent: Fix a possible crash in arp responder"
Merge "Avoid constructing a RouterInfo object to get namespace name"
Merge "Properly handle empty before/after notifications in l2pop code"
Merge "Use EUI64 for IPv6 SLAAC when subnet is specified"