adapter: Fix advertising monitor on Linux 5.12-5.17

adapter: Fix advertising monitor on Linux 5.12-5.17

The existing code assumes that, if a device supports advertising monitor
offload, DEVICE_FOUND events can be ignored since the kernel will send
ADV_MONITOR_DEVICE_FOUND events instead. Unfortunately, these new events
were added in 5.18, but offload was added in 5.12. This patch adds a
check on the MGMT API version so we can process the older DEVICE_FOUND
events when the new events are not supported.

Fixes: https://github.com/bluez/bluez/issues/357
Signed-off-by: Manika Shrivastava <manika.sh@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>