Fix server_rec references in mgs_get_ocsp_response()
During the handshake the base_server of the relevant conn_rec is
always the first vhost matching the host/port combination of the
incoming connection. By the time an OCSP response is requested
mod_gnutls may already have selected another server based on SNI, but
Apache hasn't updated the conn_rec yet. In that case c->base_server
does not refer to the right server, and if that server reference is
used to get the mod_gnutls configuration it'll be the wrong one.
That behavior caused a bug where caching a fresh OCSP response during
handshake failed if the initial vhost had OCSP stapling disabled,
because with stapling disabled the cache lifetime is set to -1. In
other cases a wrong cache lifetime might have been used.
The bug is fixed by using the mod_gnutls server configuration
referenced by the mod_gnutls connection structure, which has already
been updated by the SNI parsing code. It contains a reference to the
correct server_rec.
This commit also contains a regression test.
