Clean up default aliases

Removes 192.168.1.20 plug alias from /etc/config/network and adds a necessary dnsmasq config reload to 90-thisnode hotplug script.

To test:
0. Disconnect from wireless on test computer.
1. On first boot, before running quickstart, connect via static 192.168.1.x address and ping 192.168.1.20. Ping should fail.
2. Reconnect via dhcp and point browser to "thisnode". Connection should succeed.
3. Run quickstart
4. Connect to thisnode using wired interface. Connection should succeed.
5. Remove ethernet cable and connect to AP. Should still be able to connect to "thisnode"