miniupnpd: fix error message during shutdown

During shutdown, miniupnpd is stopped after network. Because of this,
miniupnpd is unable to broadcast good-bye notifications, and displays an
error message. Stop miniupnpd before netifd to solve this.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
Merge pull request #67 from stintel/miniupnpd_shutdown_order

miniupnpd: fix error message during shutdown