Bluetooth: btintel: Add combined set_diag functions

This patch adds a combined set_diag functions.
It also changes the btintel_set_diag_mfg() to static since it is no
longer used by others.

Signed-off-by: Tedd Ho-Jeong An <tedd.an@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>