Bump mbedTLS version to 2.16.4

Origin: ARMmbed/mbedTLS
License: Apache-2.0
URL: https://github.com/ARMmbed/mbedtls/releases/tag/mbedtls-2.16.4
commit: 39e2c0eeb6501980764793e8d54c49c0a42bde48
Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>