xfs_db: version command misses RMAPBT feature string

xfs_db: version command misses RMAPBT feature string

When I create a XFS with "rmapbt=1,reflink=1", "xfs_db -c version"
didn't show RMAPBT feature. But REFLINK can be found.

  # mkfs/mkfs.xfs -f -m rmapbt=1,reflink=1 /dev/sda3
  # db/xfs_db -c version /dev/sda3
  versionnum [0xb4a5+0x18a] = V5,NLINK,DIRV2,ALIGN,LOGV2,EXTFLG,MOREBITS,
                  ATTR2,LAZYSBCOUNT,PROJID32BIT,CRC,FTYPE,FINOBT,REFLINK

Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>