network: fix active connection state sync issue

Refactor code, add locker for each dbus properties,
and fix dbus property connecting issue that we should
append one line to re-get the target property's value
after ConnectChanged(), like following:

    nmAConn.State.ConnectChanged(func() {
        aconn.State = nmAConn.State.Get()
    })
    aconn.State = nmAConn.State.Get()

tower: https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/c82b9fd4b1d648f7abb579222baeccf3/
tower: https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/5c9cf29f29f4466e8edd1efba286a237/
Change-Id: I012bd59fe270785ed740562f0d78cfed563def4a