Bluetooth: Rename mgmt_inquiry_failed()

This patch renames the function mgmt_inquiry_failed() to
mgmt_start_discovery_failed(). This function is more related
to MGMT_OP_START_DISCOVERY command handling than to inquiry.
Besides, this functions will be reused by LE based discovery
procedures in case of failure.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>