In case of UATT, if a connection was lost while user was holding a read
or write attribute callback, `bt_l2cap_send_pdu` (called from
`att.c::chan_send`) will anyway queue a PDU and trigger tx work. The PDU
won't be sent eventually, but neither will hold an error code, which
will allow it to bypass the error check in `att_on_sent_cb` and call
`att_sent` function.
For EATT `bt_l2cap_chan_send` is used which already handles this case
and the error code is passed to `att_on_sent_cb`.
This change adds connection state check to `bt_l2cap_send_pdu`
preventing from unnecessary code execution when connection does not
exist anymore.
Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>
74972e694b