[client] Code cleaning in net pkg and fix exit node feature on Android(#2932)

Code cleaning around the util/net package. The goal was to write a more understandable source code but modify nothing on the logic.
Protect the WireGuard UDP listeners with marks.
The implementation can support the VPN permission revocation events in thread safe way. It will be important if we start to support the running time route and DNS update features.

- uniformize the file name convention: [struct_name] _ [functions] _ [os].go
- code cleaning in net_linux.go
- move env variables to env.go file

go.sum

@@ -527,8 +527,8 @@ github.com/netbirdio/service v0.0.0-20240911161631-f62744f42502 h1:3tHlFmhTdX9ax
 github.com/netbirdio/service v0.0.0-20240911161631-f62744f42502/go.mod h1:CIMRFEJVL+0DS1a3Nx06NaMn4Dz63Ng6O7dl0qH0zVM=
 github.com/netbirdio/signal-dispatcher/dispatcher v0.0.0-20241010133937-e0df50df217d h1:bRq5TKgC7Iq20pDiuC54yXaWnAVeS5PdGpSokFTlR28=
 github.com/netbirdio/signal-dispatcher/dispatcher v0.0.0-20241010133937-e0df50df217d/go.mod h1:5/sjFmLb8O96B5737VCqhHyGRzNFIaN/Bu7ZodXc3qQ=
-github.com/netbirdio/wireguard-go v0.0.0-20241107152827-57d8513b5f73 h1:jayg97LH/jJlvpIHVxueTfa+tfQ+FY8fy2sIhCwkz0g=
-github.com/netbirdio/wireguard-go v0.0.0-20241107152827-57d8513b5f73/go.mod h1:tkCQ4FQXmpAgYVh++1cq16/dH4QJtmvpRv19DWGAHSA=
+github.com/netbirdio/wireguard-go v0.0.0-20241125150134-f9cdce5e32e9 h1:Pu/7EukijT09ynHUOzQYW7cC3M/BKU8O4qyN/TvTGoY=
+github.com/netbirdio/wireguard-go v0.0.0-20241125150134-f9cdce5e32e9/go.mod h1:tkCQ4FQXmpAgYVh++1cq16/dH4QJtmvpRv19DWGAHSA=
 github.com/nicksnyder/go-i18n/v2 v2.4.0 h1:3IcvPOAvnCKwNm0TB0dLDTuawWEj+ax/RERNC+diLMM=
 github.com/nicksnyder/go-i18n/v2 v2.4.0/go.mod h1:nxYSZE9M0bf3Y70gPQjN9ha7XNHX7gMc814+6wVyEI4=
 github.com/nxadm/tail v1.4.4/go.mod h1:kenIhsEOeOJmVchQTgglprH7qJGnHDVpk1VPCcaMI8A=