device: Reply ATT requests during bonding
device: Reply ATT requests during bonding

Unlike BR/EDR which has a dynamically allocated L2CAP data channel, LE
has a fixed L2CAP channel where data are transmitted (CID 4). This means
that once the LE link is established the remote device is able to send
data (ATT messages) to the local device.

Due to the ATT sequential request-response protocol, once a client sends
a request to a server, that client shall send no other request to the
same server until a response PDU has been received. If the response PDU
arrives in 30 secs the remote device disconnects.

This way, in order to be able to reply ATT requests which may come
through channel ID 4 during the pairing, we first establish an ATT
connection and then we start the pairing process.

That issue was discovered during test sessions in UPF. We found some LE
devices sending ATT Requests in CID 4 while pairing was still in
progress

silent-snowman/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,ComputeCycles/bluez,ComputeCycles/bluez,pkarasev3/bluez,silent-snowman/bluez,mapfau/bluez,mapfau/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez