mwgc: fix communication to remote groundstations

Since commit b07024244d5a4961fa9641fab4e9f6ad601f1c58 the following
didn't work anymore:

   mwgc-1.1 -s /dev/ttyACM0 -ip 172.20.0.102

The setup is as follows: arduino promicro -> usb -> SAMA5D3  xplained
(172.20.0.160) -> UDP -> laptop (172.20.0.102)

I left the flighsimulator address alone, since that has a comment saying
it needs to be on localhost.

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>