Reject extraneous data after SSL encryption handshake.

Reject extraneous data after SSL encryption handshake.

In the server side implementation of SSL negotiation
(pool_ssl_negotiate_serverclient()), it was possible for a
man-in-the-middle attacker to inject arbitrary SQL commands. This is
possible if Pgpool-II is configured to use cert authentication or
hostssl + trust. This resembles PostgreSQL's CVE-2021-23214.

Similarly, in the client side implementation of SSL negotiation
(pool_ssl_negotiate_clientserver()), it was possible for a
man-in-the-middle attacker to inject arbitrary responses. This is
possible if PostgreSQL is using trust authentication with a clientcert
requirement. It is not possible with cert authentication because
Pgpool-II does not implement the cert authentication between Pgpool-II

To fix these reject extraneous data in the read buffer after SSL
encryption handshake.
and PostgreSQL. This resembles PostgreSQL's CVE-2021-23222.