repair: access helpers for on-disk inobt record freecount

repair: access helpers for on-disk inobt record freecount

The on-disk inobt record has two formats depending on whether sparse
inode support is enabled or not. If so, the freecount field is a single
byte and does not require byte-conversion. Otherwise, it is a 4-byte
field and does.

Create the inorec_[get|set]_freecount() helpers to abstract this detail
away from the core repair code.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>