Fix use of SSL session TransportInfo after txn is detached

Fix use of SSL session TransportInfo after txn is detached

Summary:
De-couple TransportInfo fields from SSL session structs to avoid
dangling pointers.

Facebook:
We sometimes lazily copy TransportInfo in handler after
detachClientTransaction for logging. If the socket is closed, then this
creates dangling pointers to some SSL structs. This is an attempt to fix
that.

This is similar to what @ajitb did in
https://phabricator.fb.com/D1666951 which had to be abandoned because of
memory overhead. Here, instead of copying the relevant fields per
transaction, we are only doing it once per session (shared_ptr), so the
memory overhead should be negligible.

Test Plan: Unit tests pass. Will canary

Reviewed By: afrind@fb.com

Subscribers: fugalh, bmatheny, ssl-diffs@, folly-diffs@, ajitb

FB internal diff: D1757318

Tasks: 5865651, 5879508

Signature: t1:1757318:1420482488:9f5144b499eb2086cf2a80243328db5715b48f88