Bluetooth: Fix LE L2CAP Connect Request handling together with SMP

Unlike BR/EDR, for LE when we're in the BT_CONNECT state we may or may
not have already have sent the Connect Request. This means that we need
some extra tracking of the request. This patch adds an extra channel
flag to prevent the request from being sent a second time.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>