Minor man-page formatting fixes

fB -> \fB in zpool.8 (Properties -> cachefile)
\fN -> \fB in zfs-module-parameters.5 (zfs_dirty_data_max_max_percent)
Three | -> \fR|\fI fixes for arguments of diff and inherit in zfs.8.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Signed-off-by: Haakan T Johansson <f96hajo@chalmers.se>
Closes #5645