QGC connection doubled when using topside as DHCP client

[joaoantoniocardoso]

Since #3254:

This indeed makes QGC connection doubled:

1. First, clean all QGC stuff:

\rm -rf \
  ~/.cache/QGroundControl.org \
  ~/.cache/QGCMapCache300 \
  ~/Documents/QGroundControl \
  ~/.config/QGroundControl.org

2. Then, use the following setup:

• Vehicle with static IP (192.168.2.2) + DHCP Server (192.168.2.x)
• Topside computer as DHCP client (leased as 192.168.2.184)

3. Then, when opening QGC:

• QGC connects immediately
• QGC finds and shows the video stream + video controls
• QGC reports Heartbeat and other messages at doubled rate (heartbeat at 2Hz, etc)
• Text messages are all doubled:

4. If I remove one of the IPs, the messages are then at normal rate (not doubled)

Originally posted by @joaoantoniocardoso in #3509 (review)