iw: bitrate: support link id

For MLD, support to assign link-id field. For non-MLD, just as before,
no need to assign it. If going to assign link-id field, need to place
it at the beginning of argv (i.e. right after "set bitrates").

	set bitrates [link-id <LINK ID>] ...

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Link: https://patch.msgid.link/20250922071017.11954-5-kevin_yang@realtek.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>