LU-2681 fld: shrink seq_type in lsr_flags

LU-2681 fld: shrink seq_type in lsr_flags

In lu_seq_range, lsr_flags is treated to only hold LU_SEQ_RANGE_MDT,
LU_SEQ_RANGE_OST or LU_SEQ_RANGE_ANY.  Because they can fit into two
bits, using lsr_flags(32 bits) is clearly unnecessary.

This patch will shrink the current seq_type to 2 bits, so other flags
can be used in lsr_flags in future.  Add wrapper functions to access
and set the flags:

 fld_range_set_mdt(), fld_range_set_ost(), fld_range_set_any()
 fld_range_is_mdt(), fld_range_is_ost(), fld_range_is_any()

If another target type were needed, it could potentially use
LU_SEQ_RANGE_FOO 0x2, which is currently unused.

Signed-off-by: Wang Di <di.wang@intel.com>
Change-Id: I721c9fe5778ee331d3f77ac885f3b482e2322c85
Reviewed-on: http://review.whamcloud.com/5999
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>