MINOR: ssl: move certificate selection in a dedicate function

MINOR: ssl: move certificate selection in a dedicate function

The certificate selection used in the WolfSSL cert_cb and in the OpenSSL
clienthello callback is the same, the function was duplicate to achieve
the same.

This patch move the selection code to a common function called
ssl_sock_chose_sni_ctx().

The servername string is still lowered in the callback, however the
search for the first dot in the string (wildp) is done in
ssl_sock_chose_sni_ctx()

The function uses the same certificate selection algorithm as before, it
needs to know if you need rsa or ecdsa, the bind_conf to achieve the
lookup, and the servername string.

This patch moves the code for WolSSL only.