v4l2 update function, video source size change, "check" unit test system integration

This part of the project on dynamic change the resolution depending on the quality of the communication channel. v4l can change resolution of the cam, so, i think this is a useful feature.
This can cause errors in the already implemented update handlers of vidsrc (although they are unknown to me). Moreover, the structure "vidsrc_prm" is a container  containing new parameters of source. It seems logical to put the new size there. I would add another option there that specifies what exactly changed. This will leave an opportunity to extend the functionality.

enum {
VIDSRC_ORITNT = 1,
VIDSRC_FPS = 2,
VIDSRC_SIZE = 4
};

struct vidsrc_prm {
int orient;
int fps;
struct vidsz *size;
uint32_t prm; /* eg VIDSRC_FPS | VIDSRC_SIZE */
};
As for the conventional method (mem_deref & vidsrc_alloc) - to call the vidsrc_alloc i must to know the address of frame handler, but i don't know how to get it without breaking the encapsulation of video source module.