string to lookup using getservbyname() and a string table.
BIO_set_accept_port() uses the string B<port> to set the accept
-port. "port" has the same syntax as the port specified in
+port of BIO I<b>. "port" has the same syntax as the port specified in
BIO_set_conn_port() for connect BIOs, that is it can be a numerical
port string or a string to lookup using getservbyname() and a string
table.