P2P: Fix the setter function for DBus group properties

P2P: Fix the setter function for DBus group properties

The setter function uses the same hostapd_data structure as the getter
which causes it to crash if called on a P2P client. To overcome this
issue, the role is checked to ensure it is called on a group owner and
the pointer is examined for validity. The function will return an error
if called on a non-GO system.

Signed-hostap: Todd Previte <toddx.a.previte@intel.com>
Signed-hostap: Angie Chinchilla <angie.v.chinchilla@intel.com>
intended-for: hostap-1