populate port security default into network

populate port security default into network

Previously, the default value would be populated into attr by API
controller, but some codes in plugin or service plugins call plugin
to create network directly, such as l3, which will have no default
value populated.
This patch fixes it by populating default port_security value into
network data.

In addition, for network without port-security set, we also give the
default value to populate the return network dict object, which will
let the extension construct the response dictionary gracefully for
those existing network.

Co-Authored-By: gong yong sheng <gong.yongsheng@99cloud.net>
Change-Id: I73abc98d83372f6259f17680806e6541458e2077
Closes-bug: #1461519
Closes-Bug: #1461647
Closes-Bug: #1468588