Feature/exit node Android (#1916)

Support exit node on Android.
With the protect socket function, we mark every connection that should be used out of VPN.

client/internal/dns/upstream_general.go

@@ -0,0 +1,38 @@
+//go:build !android && !ios
+
+package dns
+
+import (
+	"context"
+	"net"
+	"time"
+
+	"github.com/miekg/dns"
+
+	"github.com/netbirdio/netbird/client/internal/peer"
+)
+
+type upstreamResolver struct {
+	*upstreamResolverBase
+}
+
+func newUpstreamResolver(
+	ctx context.Context,
+	_ string,
+	_ net.IP,
+	_ *net.IPNet,
+	statusRecorder *peer.Status,
+	_ *hostsDNSHolder,
+) (*upstreamResolver, error) {
+	upstreamResolverBase := newUpstreamResolverBase(ctx, statusRecorder)
+	nonIOS := &upstreamResolver{
+		upstreamResolverBase: upstreamResolverBase,
+	}
+	upstreamResolverBase.upstreamClient = nonIOS
+	return nonIOS, nil
+}
+
+func (u *upstreamResolver) exchange(ctx context.Context, upstream string, r *dns.Msg) (rm *dns.Msg, t time.Duration, err error) {
+	upstreamExchangeClient := &dns.Client{}
+	return upstreamExchangeClient.ExchangeContext(ctx, r, upstream)
+}