BUG/MEDIUM: ssl: bad auth selection with TLS1.2 and WolfSSL

BUG/MEDIUM: ssl: bad auth selection with TLS1.2 and WolfSSL

The ClientHello callback for WolfSSL introduced in haproxy 2.9, seems
not to behave correctly with TLSv1.2.

In TLSv1.2, this is the cipher that is used to chose the authentication algorithm
(ECDSA or RSA), however an SSL client can send a signature algorithm.

In TLSv1.3, the authentication is not part of the ciphersuites, and
is selected using the signature algorithm.

The mistake in the code is that the signature algorithm in TLSv1.2 are
overwritting the auth that was selected using the ciphers.

This must be backported as far as 2.9.