CLEANUP: ssl: rename ssl_sock_load_ca to ssl_sock_gencert_load_ca

CLEANUP: ssl: rename ssl_sock_load_ca to ssl_sock_gencert_load_ca

ssl_sock_load_ca is defined in ssl_gencert.c and compiled only if
SSL_NO_GENERATE_CERTIFICATES is not defined. It's name is a bit confusing, as
we may think at the first glance, that it's a generic function, which is also
used to load CA file, provided via 'ca-file' keyword.
ssl_set_verify_locations_file is used in this case.

So let's rename ssl_sock_load_ca into ssl_sock_gencert_load_ca. Same is
applied to ssl_sock_free_ca.