Bluetooth: Fixes FindMe Target L2CAP channel issue

When whitelist APIs are used for establishing LE connection
between the phone and remote LE device, few times
ATT requests like Read by Group Type request are received by
the phone from the remote device before the L2CAP channel has
been set up completely. Hence the LE server in the phone
sends a "Request not supported" error response since
the L2CAP channel has not yet been created. This fix checks
the state of the L2CAP channel after sleeping for a while
and sends the ATT request to be processed by the upper layers
when the L2CAP channel is up.

CRs-fixed: 415648

Change-Id: Ifbaf75fe612195b3c6ce49629106cac09dd0a437
Signed-off-by: Subramanian Srinivasan <subrsrin@codeaurora.org>
Signed-off-by: Mallikarjuna GB <gbmalli@codeaurora.org>