Kit: Adapter: ignore error when updating tunnel settings in offline

Since around iOS 15.1, calling `setNetworkSettings()` when in
airplane mode, throws an unknown error:

Error Domain=NEAgentErrorDomain Code=1

Signed-off-by: Andrej Mihajlov <and@mullvad.net>

Sources/WireGuardKit/WireGuardAdapter.swift

@@ -253,12 +253,27 @@ public class WireGuardAdapter {
                 self.packetTunnelProvider?.reasserting = false
             }
 
+            let settingsGenerator: PacketTunnelSettingsGenerator
             do {
-                let settingsGenerator = try self.makeSettingsGenerator(with: tunnelConfiguration)
-                try self.setNetworkSettings(settingsGenerator.generateNetworkSettings())
+                settingsGenerator = try self.makeSettingsGenerator(with: tunnelConfiguration)
+            } catch let error as WireGuardAdapterError {
+                completionHandler(error)
+                return
+            } catch {
+                fatalError()
+            }
 
             switch self.state {
             case .started(let handle, _):
+                do {
+                    try self.setNetworkSettings(settingsGenerator.generateNetworkSettings())
+                } catch let error as WireGuardAdapterError {
+                    completionHandler(error)
+                    return
+                } catch {
+                    fatalError()
+                }
+
                 let (wgConfig, resolutionResults) = settingsGenerator.uapiConfiguration()
                 self.logEndpointResolutionResults(resolutionResults)
 
@@ -270,6 +285,19 @@ public class WireGuardAdapter {
                 self.state = .started(handle, settingsGenerator)
 
             case .temporaryShutdown:
+                // On iOS 15.1 or newer, updating network settings may fail when in airplane mode.
+                // Network path monitor will retry updating settings later when connectivity is
+                // back online.
+                do {
+                    try self.setNetworkSettings(settingsGenerator.generateNetworkSettings())
+                } catch let error as WireGuardAdapterError {
+                    if case .setNetworkSettings(let systemError) = error {
+                        self.logHandler(.verbose, "Failed to set network settings while offline. Will retry when connectivity is back online. Error: \(systemError.localizedDescription)")
+                    }
+                } catch {
+                    fatalError()
+                }
+
                 self.state = .temporaryShutdown(settingsGenerator)
 
             case .stopped:
@@ -277,11 +305,6 @@ public class WireGuardAdapter {
             }
 
             completionHandler(nil)
-            } catch let error as WireGuardAdapterError {
-                completionHandler(error)
-            } catch {
-                fatalError()
-            }
         }
     }