Bluetooth PAN: Set isPreferred to true (1/2)

isPreferred must always be true for PAN so that the DUT can initiate
a PANU connection with the remote device not only from the internet
access menu in the profile setting, but also from the paired device
list menu.

Currently isPreferred is only true when PAN is in connected state
for the PANU role, so it will return false when the PAN profile is
not connected and the PANU connection will never be initiated
from the paired device list menu.

Change-Id: I120e681a113f56b74b45e01870adf96cdc2ca262