This commit adds varios fixes for the implementation of hybrid
certificates with two algorithms:
* Support for Certificate Signing Requests (both creating hybrid ones
and also verifying ones)
* Fix for SAN fields in the DecodedCert and PreTBS generation
* Fix related to WOLFSSL_SMALL_STACK
Signed-off-by: Tobias Frauenschläger <t.frauenschlaeger@me.com>