xfs: Convert xfs_attr_sf macros to inline functions

xfs: Convert xfs_attr_sf macros to inline functions

Source kernel commit: e01b7eed5d0a9b101da53701e92136c3985998af

xfs_attr_sf_totsize() requires access to xfs_inode structure, so, once
xfs_attr_shortform_addname() is its only user, move it to xfs_attr.c
instead of playing with more #includes.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>