greybus: tracing: add interface mode_switch

Add the value of an interface's mode_switch field to the information
tracked and reported for tracing.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>