hotfix(pmtud): detect IPv6 usage in VPN connection

internal/pmtud/ip/source.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"fmt"
 	"net/netip"
-	"strings"
 
 	"github.com/jsimonetti/rtnetlink"
 	"github.com/qdm12/gluetun/internal/pmtud/constants"
@@ -28,10 +27,7 @@ func SrcAddr(dst netip.AddrPort, proto int) (src netip.AddrPort, cleanup func(),
 	return netip.AddrPortFrom(srcAddr, srcPort), cleanup, nil
 }
 
-var (
-	errNoRoute            = errors.New("no route to destination")
-	ErrNetworkUnreachable = errors.New("network unreachable")
-)
+var errNoRoute = errors.New("no route to destination")
 
 func srcIP(dst netip.Addr) (netip.Addr, error) {
 	conn, err := rtnetlink.Dial(nil)
@@ -54,9 +50,6 @@ func srcIP(dst netip.Addr) (netip.Addr, error) {
 	}
 	messages, err := conn.Route.Get(requestMessage)
 	if err != nil {
-		if strings.Contains(err.Error(), "network is unreachable") {
-			err = ErrNetworkUnreachable
-		}
 		return netip.Addr{}, fmt.Errorf("getting routes to %s: %w", dst, err)
 	}