get the remote banner
const char *libssh2_session_banner_get(oLIBSSH2_SESSION *session);
Once the session has been setup and libssh2_session_handshake(3)
completed successfully, this function can be used to get the server id from
the banner each server presents.
A pointer to a string or NULL if something failed. The data pointed to will be
allocated and associated to the session handle and will be freed by libssh2
Added in 1.4.0