zpool_load_compat() should create strings of length ZFS_MAXPROPLEN
Otherwise, strlcat() can overflow them.
Coverity found this.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Neal Gompa <ngompa@datto.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13866