android: Announce support for TFC padding

Has been supported by libipsec for a long time (since 5.1.1).  UDP encap
is already enforced via config, this just makes the flags the same as
in kernel-libipsec.

src/frontends/android/app/src/main/jni/libandroidbridge/kernel/android_ipsec.c

@@ -49,7 +49,8 @@ static void expire(uint8_t protocol, uint32_t spi, host_t *dst, bool hard)
 METHOD(kernel_ipsec_t, get_features, kernel_feature_t,
 	private_kernel_android_ipsec_t *this)
 {
-	return KERNEL_SA_USE_TIME;
+	return KERNEL_REQUIRE_UDP_ENCAPSULATION | KERNEL_ESP_V3_TFC |
+		   KERNEL_SA_USE_TIME;
 }
 
 METHOD(kernel_ipsec_t, get_spi, status_t,