P9fs linux compatibility issues

The propolis P9fs device seems to have some compatibility issues with Linux guests. I noticed this just now in the guest.

# ls -lh
ls: droute.sh: Link number out of range
ls: dummy-routes.sh: Link number out of range
ls: dummy-routes2.sh: Link number out of range
ls: frr-bgp.txt: Link number out of range
ls: init.sh: Link number out of range
total 37K
-rw-r--r-- 1 root root 86K Aug 26 19:43 droute.sh
-rwxr-xr-x 1 root root 43K Aug 26 19:37 dummy-routes.sh
-rwxr-xr-x 1 root root 43K Aug 26 19:37 dummy-routes2.sh
-rw-r--r-- 1 root root 49K Aug 26 05:40 frr-bgp.txt
-rwxr-xr-x 1 root root 745 Aug 26 19:19 init.sh

There also seem to be problems reading some files that just return an error when read.

cat droute.sh
cat: droute.sh: Invalid argument

# stat droute.sh
  File: droute.sh
  Size: 87274           Blocks: 23         IO Block: 87552  regular file
Device: 25h/37d Inode: 14738623    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2024-08-26 19:43:49.708973469 +0000
Modify: 2024-08-26 19:43:24.943289406 +0000
Change: 2024-08-26 19:43:24.943289406 +0000
 Birth: -

Reproduce the P9fs compatibility problems in a Linux guest using the shown ls, cat, and stat commands. Inspect the P9fs device handling and determine why directory listings report “Link number out of range” and file reads return “Invalid argument”; done means these files can be listed and read successfully.