Bluetooth: Fix multiple LE socket handling

Bluetooth: Fix multiple LE socket handling

The LE ATT server socket needs to be superseded by any ATT client
sockets. Previously this was done by looking at the hcon->out variable
(indicating whether the connection is outgoing or incoming) which is a
too crude way of determining whether the server socket needs to be
picked or not (an outgoing connection doesn't necessarily mean that an
ATT client socket has triggered it).

This patch extends the ATT server socket lookup function
(l2cap_le_conn_ready) to be used for all LE connections (regardless of
the hcon->out value) and adds an internal check into the function for
the existence of any ATT client sockets (in which case the server socket
should be skipped). For this to work reliably all lookups must be done
while the l2cap_conn->chan_lock is held, meaning also that the call to
l2cap_chan_add needs to be changed to its lockless __l2cap_chan_add
counterpart.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>