Move Decrypting Session Ticket to Different Function

[maddeleine]

Problem:

The function s2n_set_handshake_type is currently where we decrypt the session ticket on the server side in tls12. This a pretty weird place for it because the function is now doing more than its name says it's doing.

Solution:

Move the processing logic from that function somewhere more appropriate, like the establish_session function. This should include both stateful and stateless session ticket decrypting.

• Does this change what S2N sends over the wire? No
• Does this change any public APIs? No
• Which versions of TLS will this impact?
  TLS12

Requirements / Acceptance Criteria:

Refactor of s2n_set_handshake_type

• RFC links: N/A
• Related Issues: N/A
• Will the Usage Guide or other documentation need to be updated? N/A
• Testing: Make sure all the functionality stays the same.
  • Will this change trigger SAW changes? No
  • Should this change be fuzz tested? No

Out of scope:

Is there anything the solution will intentionally NOT address?