tls: get cipher_name from cipher_desc in tls_set_sw_offload

tls_cipher_desc also contains the algorithm name needed by
crypto_alloc_aead, use it.

Finally, use get_cipher_desc to check if the cipher_type coming from
userspace is valid, and remove the cipher_type switch.

Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lore.kernel.org/r/53d021d80138aa125a9cef4468aa5ce531975a7b.1692977948.git.sd@queasysnail.net


Signed-off-by: Jakub Kicinski <kuba@kernel.org>