wgengine/magicsock: give pinger a more generous packet timeout.

The first packet to transit may take several seconds to do so, because
setup rates in wgengine may result in the initial WireGuard handshake
init to get dropped. So, we have to wait at least long enough for a
retransmit to correct the fault.

Signed-off-by: David Anderson <danderson@tailscale.com>

wgengine/magicsock/magicsock_test.go

@@ -722,7 +722,13 @@ func newPinger(t *testing.T, logf logger.Logf, srcM, dstM *magicStack, srcIP, ds
 		select {
 		case <-dstM.tun.Inbound:
 			return true
-		case <-time.After(time.Second):
+		case <-time.After(10 * time.Second):
+			// Very generous timeout here because depending on
+			// magicsock setup races, the first handshake might get
+			// eaten by the receiving end (if wireguard-go hasn't been
+			// configured quite yet), so we have to wait for at least
+			// the first retransmit from wireguard before we declare
+			// failure.
 			t.Errorf("timed out waiting for ping to transit")
 			return true
 		case <-ctx.Done():