v4l2

1) update handler
2) video source resolution change
3) control of second v4l2 instance creation

	modified:   include/baresip.h
	modified:   modules/v4l2/v4l2.c
ua - ua_hungup_other_calls fixed to have worked with multiple accounts

	modified:   src/ua.c
silent calls are terminated after timeout

	modified:   include/baresip.h
	modified:   src/config.c
	modified:   src/core.h
	modified:   src/stream.c