tls: extend tls_cipher_desc to fully describe the ciphers

- add nonce, usually equal to iv_size but not for chacha
 - add offsets into the crypto_info for each field
 - add algorithm name
 - add offloadable flag

Also add helpers to access each field of a crypto_info struct
described by a tls_cipher_desc.

Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lore.kernel.org/r/39d5f476d63c171097764e8d38f6f158b7c109ae.1692977948.git.sd@queasysnail.net


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