This can happen, e.g., when a P2P client connects to a P2P group
using the infrastructure WLAN interface instead of P2P group
interface. In that case, the P2P client may behave as if the GO
would be a P2P Manager WLAN AP.
If enabled, cross connection allows GO to forward IPv4 packets
using masquerading NAT from the P2P clients in the group to an
uplink WLAN connection. This is disabled by default and can be
enabled with "wpa_cli p2p_set cross_connect 1" on the P2P device
interface.
While there is no real value in this, the spec seems to mark this
attribute as mandatory from GO, so better included it regardless
of whether we have clients or not (the attribute is empty in case
no clients are connected).
