introspection: Alow to not define interface subclass
introspection: Alow to not define interface subclass

Change-Id: I7bdb77743e01ac351a7a0f9e07fcfc4b61949d04
Signed-off-by: Krzysztof Opasiak <8064eda6f94b3817252b7d7649cf754592f63500@samsung.com>

gadgetd/gadgetd,gadgetd/gadgetd,gadgetd/gadgetd