tls: keep credentials when HTTP reconnects

tls: keep credentials when HTTP reconnects

Keeping the credentials container saves some times, as we do not need
to load and parse all of the 100+ Certificate Authorities again.
In the future, it will also avoid reloading the stored public keys
(i.e. security exceptions), or asking for user confirmation again.

Given how the HTTP access is written, the credentials are now preserved
upon seeking. Unfortunately, they are not recycled across redirections
as access_t.p_sys gets destroyed internally. This also does not work
across multiple inputs - support from the instance or input manager
would be required.