wwan: core: add print for wwan port attach/disconnect

Refer to USB serial device or net device, there is a notice to
let end user know the status of device, like attached or
disconnected. Add attach/disconnect print for wwan device as
well.

Signed-off-by: Slark Xiao <slark_xiao@163.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Link: https://lore.kernel.org/r/20230420023617.3919569-1-slark_xiao@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>