P9fs linux compatibility issues

[rcgoodfellow]

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: -