removed duplicated code in get_ callbacks
removed duplicated code in get_ callbacks

added a get_link internal callback to eliminate the duplicated code in _get
functions.

Signed-off-by: Luotao Fu <85ed96e8394e24a331a1a2a9131a782ad665de22@pengutronix.de>

lalten/libsocketcan,lalten/libsocketcan,lalten/libsocketcan