BUG/MINOR: ssl: fix a double-free of the .sctl buffer with several contexts

BUG/MINOR: ssl: fix a double-free of the .sctl buffer with several contexts

ssl_sock_load_sctl() stores the ckch's .sctl buffer in SSL_CTX ex_data,
whose free callback releases it when the context is destroyed. The ckch
also frees this buffer, causing a double-free during deinit or "haproxy -c",
even with a single bind and certificate. Sharing the certificate across
contexts adds further frees of the same buffer.

Give each context its own copy, leaving the original owned by the ckch.
AWS-LC already copies the list through its native API.

This bug was introduced in 2.1 by commit 0dfae6c315 ("MINOR: ssl: load sctl
from buf OR from a file") and must be backported to all versions since then.