The server sends the UDP packets via the wrong interface.

[TByte007]

Describe the bug
When my brother (or whoever) connects on the outside interface this happens:
The packets are coming via home0 which has 10.0.0.1/24 network:
#:> tcpdump -ni home0 host 10.0.0.2 and port 21116
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on home0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
23:47:10.303677 IP 10.0.0.2.54467 > 10.0.0.1.21116: UDP, length 15
23:47:14.302891 IP 10.0.0.2.54467 > 10.0.0.1.21116: UDP, length 15

But are going out via aone0 which has the real IP to the ISP.

#:> tcpdump -ni aone0 host 10.0.0.2 and port 21116
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on aone0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
23:45:39.300826 IP 10.0.0.1.21116 > 10.0.0.2.50965: UDP, length 4
23:45:42.300950 IP 10.0.0.1.21116 > 10.0.0.2.50965: UDP, length 4

The only way to "fix" it is to restart the demons (hbbs/hbbr) and connect BEFORE my brother. Basically whoever is first only he can connect.
I'm guessing it somehow binds/connects the socket including the interface or i have no idea what is going on exactly.

Describe the environment
FreeBSD 14.0 router, no dockers or anything.
How to Reproduce the bug
explained in the description

Expected behavior
I should be able to connect from both the inside and the outside interfaces.

[sierja]

I have confirmed this problem exists on the Docker based version of HBBS in host network mode as well.

@rustdesk
I think the problem is probably caused by the use of FramedSocket in handle_udp when it's listening on an unspecified address (0.0.0.0) then sending a reply as it's then left up to the OS to choose an interface. The workaround for those impacted by this bug is not to use Rustdesk HBBS with multiple interfaces/IPs.

When coding a fix, please consider those that need to have Rustdesk listening on multiple interfaces at the same time (as opposed to tying it to one interface/IP)