LU-1876 ldlm: extend ldlm_valblock_ops{}

LU-1876 ldlm: extend ldlm_valblock_ops{}

To extend the usage of RQF_DLM_LVB for quota, layout lock and nano
seconds, two extra callbacks will be added:
 - lvbo_size: determine the size of lvb data
 - lvbo_fill: fill in RPC buffer by lvb data

Also framework of mdt_lvb is added for future extension.

Signed-off-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Change-Id: I2b3022525f8fbef72549a25766aa73d94b8b997c
Reviewed-on: http://review.whamcloud.com/3960
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>