DOC: Protocol doc: add SSL TLVs, rename CHECKSUM

Add SSL-related TLV types PP2_SUBTYPE_SSL_CIPHER,
PP2_SUBTYPE_SSL_SIG_ALG and PP2_SUBTYPE_SSL_KEY_ALG. Rename
PP2_TYPE_CHECKSUM to PP2_TYPE_CRC32C to make it easier to add checksums
using other algorithms. Clarified encoding of the string fields.
Renamed ASCII to US-ASCII as recommended by
https://www.iana.org/assignments/character-sets/character-sets.xhtml.
1 file changed