Add the get device flags and set device flags mgmt ops and the device
flags changed event. Their behavior is described in detail in
mgmt-api.txt in bluez.

Sample btmon trace when a HID device is added (trimmed to 75 chars):

@ MGMT Command: Unknown (0x0050) plen 11        {0x0001} [hci0] 18:06:14.98
        90 c5 13 cd f3 cd 02 01 00 00 00                 ...........
@ MGMT Event: Unknown (0x002a) plen 15          {0x0004} [hci0] 18:06:14.98
        90 c5 13 cd f3 cd 02 01 00 00 00 01 00 00 00     ...............
@ MGMT Event: Unknown (0x002a) plen 15          {0x0003} [hci0] 18:06:14.98
        90 c5 13 cd f3 cd 02 01 00 00 00 01 00 00 00     ...............
@ MGMT Event: Unknown (0x002a) plen 15          {0x0002} [hci0] 18:06:14.98
        90 c5 13 cd f3 cd 02 01 00 00 00 01 00 00 00     ...............
@ MGMT Event: Command Compl.. (0x0001) plen 10  {0x0001} [hci0] 18:06:14.98
      Unknown (0x0050) plen 7
        Status: Success (0x00)
        90 c5 13 cd f3 cd 02                             .......
@ MGMT Command: Add Device (0x0033) plen 8      {0x0001} [hci0] 18:06:14.98
        LE Address: CD:F3:CD:13:C5:90 (Static)
        Action: Auto-connect remote device (0x02)
@ MGMT Event: Device Added (0x001a) plen 8      {0x0004} [hci0] 18:06:14.98
        LE Address: CD:F3:CD:13:C5:90 (Static)
        Action: Auto-connect remote device (0x02)
@ MGMT Event: Device Added (0x001a) plen 8      {0x0003} [hci0] 18:06:14.98
        LE Address: CD:F3:CD:13:C5:90 (Static)
        Action: Auto-connect remote device (0x02)
@ MGMT Event: Device Added (0x001a) plen 8      {0x0002} [hci0] 18:06:14.98
        LE Address: CD:F3:CD:13:C5:90 (Static)
        Action: Auto-connect remote device (0x02)
@ MGMT Event: Unknown (0x002a) plen 15          {0x0004} [hci0] 18:06:14.98
        90 c5 13 cd f3 cd 02 01 00 00 00 01 00 00 00     ...............
@ MGMT Event: Unknown (0x002a) plen 15          {0x0003} [hci0] 18:06:14.98
        90 c5 13 cd f3 cd 02 01 00 00 00 01 00 00 00     ...............
@ MGMT Event: Unknown (0x002a) plen 15          {0x0002} [hci0] 18:06:14.98
        90 c5 13 cd f3 cd 02 01 00 00 00 01 00 00 00     ...............
@ MGMT Event: Unknown (0x002a) plen 15          {0x0001} [hci0] 18:06:14.98
        90 c5 13 cd f3 cd 02 01 00 00 00 01 00 00 00     ...............
Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Reviewed-by: Alain Michaud <alainm@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>