libv4l2rds: update the list of AFs if the number of AFs changes

If the number of alternate frequencies changes, then the internal
list of such frequencies should be cleared.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
libv4l2rds: rename V4L2_RDS_FLAG_STATIC_PTY to _DYNAMIC_PTY

If the bit is 1, then the PTY is dynamic, not static as the name
suggests.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
rds-ctl: add support for dynamic/static PTY

This bit was never printed for some reason.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>