### Purpose
As discussed on the forum:
https://forum.syncthing.net/t/reviving-nat-pmp-in-v2-x-on-android-14/24554
TL;DR
Android 14+ only lets java code get the gateway IPv4 address which is
used in SyncthingNative’s NAT-PMP feature.
So I’ve added the java code to the wrapper, got the router IP address
and feeded it to SyncthingNative by setting the env var
“FALLBACK_NET_GATEWAY_IPV4”.
This revives the NAT feature:
> [Z36WU] INFO: Detected 1 NAT service
### Testing
Local build and test via Android emulator (AVD 15).