java/com/tailscale/ipn: retain peer Fragment across Activity restarts

There is no reason to recreate it for transient restarts.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

android/src/main/java/com/tailscale/ipn/Peer.java

@@ -47,6 +47,7 @@ public class Peer extends Fragment {
 
 	@Override public void onCreate(Bundle b) {
 		super.onCreate(b);
+		setRetainInstance(true);
 		fragmentCreated();
 	}