rt2x00: Move rt2x00debug_dump_frame declaration to rt2x00.h.

This allows rt2x00debug_dump_frame to be used from everywhere.

This is preparation for beacon writing clean ups.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>