Bluetooth: Relax minimum advertising interval for 5.0 controllers

The 100ms limit is only valid for controllers before version 5.0. For
a 5.0 controller the minimum is 20ms (0x00a0) which is already checked
for later in the valid_adv_param() function.

Change-Id: I0566a38ff855800d2e46e1d2c0a5c7bc9bc610cd
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>