Appease GCC sprintf warnings found on Fedora 32/GCC 10.0.1
Increase the size of DDT_NAMELEN and MNT_LINE_MAX to appease GCC
snprintf truncation warnings.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chris McDonough <chrism@plope.com>
Closes #10712
Closes #10766