ITS#7373 - TLS: do not reuse tls_session if hostname check fails

If multiple servers are specified, the connection to the first one
succeeds, and the hostname verification fails, *tls_session is not
dropped, but reused when connecting to the second server.

This is a problem with Mozilla NSS backend because another handshake
cannot be performed on the same file descriptor. From this reason,
hostname checking was moved into ldap_int_tls_connect() before
connection error handling.
