btmon: Suppress HCI vendor events

When idle, Marvell 88W8897 Bluetooth adapter fills btmon logs with:

> HCI Event: Vendor (0xff) plen 5                    [hci0] 0.300944
        05 80 00 09 00

Suppress these events with the new -V option.
https://gfiber-internal-review.googlesource.com/#/c/83000/

Change-Id: Ie2d1177abca30ddfa0df1a92cf617fa315fc3ea5
1 file changed