Bluetooth: Add SCO connection fallback

When initiating a transparent eSCO connection, make use of T2 settings
at first try. T2 is the recommended settings from HFP 1.6 WideBand
Speech. Upon connection failure, try T1 settings.

When CVSD is requested and eSCO is supported, try to establish eSCO
connection using S3 settings. If it fails, fallback in sequence to S2,
S1, D1, D0 settings.

To know which setting should be used, conn->attempt is used. It
indicates the currently ongoing SCO connection attempt and can be used
as the index for the fallback settings table.

These setting and the fallback order are described in Bluetooth HFP 1.6
specification p. 101.

Signed-off-by: Frédéric Dalleau <frederic.dalleau@linux.intel.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>