logprint: Fix printing of AGF and AGI buffers

logprint: Fix printing of AGF and AGI buffers

Currently xfs_logprint doesn't show detailed data about AGF and AGI
buffers and instead always shows "Out of space". This is because
xfs_agf_t has additional fields and padding which we never read from
disk and thus buffer length is always smaller than the size of
xfs_agf_t or xfs_agi_t respectively.

Fix the problem by only making sure we have enough data in the buffer
to contain all the information we want to print.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>