Localize remaining strings in network extension

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

WireGuard/Shared/Model/NETunnelProviderProtocol+Extension.swift

@@ -3,6 +3,14 @@
 
 import NetworkExtension
 
+enum PacketTunnelProviderError: String, Error {
+    case savedProtocolConfigurationIsInvalid
+    case dnsResolutionFailure
+    case couldNotStartBackend
+    case couldNotDetermineFileDescriptor
+    case couldNotSetNetworkSettings
+}
+
 extension NETunnelProviderProtocol {
 
     enum Keys: String {