wgengine/magicsock: remove redundant deadline from netcheck report call (#13395)

netcheck.Client.GetReport() applies its own deadlines. This 2s deadline
was causing GetReport() to never fall back to HTTPS/ICMP measurements
as it was shorter than netcheck.stunProbeTimeout, leaving no time
for fallbacks.

Updates #13394
Updates #6187

Signed-off-by: Jordan Whited <jordan@tailscale.com>

net/netcheck/netcheck_test.go

@@ -860,3 +860,15 @@ func TestNodeAddrResolve(t *testing.T) {
 		})
 	}
 }
+
+func TestReportTimeouts(t *testing.T) {
+	if ReportTimeout < stunProbeTimeout {
+		t.Errorf("ReportTimeout (%v) cannot be less than stunProbeTimeout (%v)", ReportTimeout, stunProbeTimeout)
+	}
+	if ReportTimeout < icmpProbeTimeout {
+		t.Errorf("ReportTimeout (%v) cannot be less than icmpProbeTimeout (%v)", ReportTimeout, icmpProbeTimeout)
+	}
+	if ReportTimeout < httpsProbeTimeout {
+		t.Errorf("ReportTimeout (%v) cannot be less than httpsProbeTimeout (%v)", ReportTimeout, httpsProbeTimeout)
+	}
+}