zed.d/pool_import-led.sh: fix for current zpool scripts

Also minor clean-up with folding state_to_val() into a case,
unrolling the lesser-available seq into numbers,
ignoring vdev states we don't care about,
and documentation comments

Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #11934
Closes #11935