hotplug scripts are sourced not exec'd so #!/bin/sh /etc/rc.common
doesn't pull in the functions defined in /etc/rc.common thus since
'enabled' isn't defined the following sequence always fails:

enabled miniupnpd || exit 0

Unfortunately sourcing /etc/rc.common doesn't appear to work so come up
with some alternatives.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>