libfrog: refactor online geometry queries

libfrog: refactor online geometry queries

Refactor all the open-coded XFS_IOC_FSGEOMETRY queries into a single
helper that we can use to standardize behaviors across mixed xfslibs
versions.  This is the prelude to introducing a new FSGEOMETRY version
in 5.2 and needing to fix the (relatively few) client programs.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
[sandeen: remove 5.2.1 compat hack now that we have the wrapper]
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>