Bluetooth: Host: Re-order LE L2CAP connection accept procedure

Currently, when an incoming dynamic LE L2CAP connection is requested by
a peer, the connected() callback provided by the user is raised
*before* a L2CAP_LE_CREDIT_BASED_CONNECTION_RSP is sent back to the
peer.
In some cases the user will start sending data in the connected()
callback which would be received too early by the peer.
This commit fixes this behavior by making sure the connected() callback
is raised only after the connection response has been sent to the peer.

Signed-off-by: Donatien Garnier <donatien.garnier@blecon.net>