D-Bus: Fix operations when P2P management interface is used

D-Bus: Fix operations when P2P management interface is used

Commit 21efc940f6e7f07b84b7e5c5867f3d81594c4fb0 ('wpa_supplicant: Do not
register a P2P management interface on DBus') hides the special P2P
management interface from D-Bus. However, it did not take into account
the possibility of wpa_s->dbus_path and wpa_s->dbus_new_path being NULL
in such cases on number of code paths within the D-Bus handlers. This
could result in invalid arguments (NULL path) being provided to D-Bus
functions (mainly, dbus_message_iter_append_basic) and NULL pointer
dereference when iterating over all interfaces. Either of these could
make wpa_supplicant process terminate.

Fix this by explicitly checking that the interface-specific D-Bus path
has been registered before using it anywhere with D-Bus handlers. In
addition, find the correct wpa_s instance to fix P2P operations through
D-Bus when the P2P Device interface is used.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>