MOSDOp: The functions are returned by const ref and parameters passed by ref

get_snapid(),get_snap_seq,get_pg,get_object_locator,get_version are returning
by reference and the corresponding setter is accepting the param by reference.
MOSDOp constructor is is accepting pg_t  by reference now.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
MOSDOpreply: The functions are returned by const ref and parameters passed by ref

get_oid,get_pg,get_replay_version,get_user_version are returning by reference and
corresponding setter is accepting param by reference.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
MOSDOpReply: Constructor initialization list is used to instantiate members

constructor initialization list is modified to initialize ops,oid,pgid with
copy constructor instead of assignment operator in the constructor body.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
OSD: pass param by ref to avoid copying overrhead

passing OpRequestRef, OSDMapRef by ref to avoid refcounting overhead
and in some cases passing structures by const ref.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
OSDMap: avoid passing pg_t by value

Passing pg_t param by cons ref for avoiding copies.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
PG: pass OpRequestRef by ref to avoid refcounting overhead

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
PG::op_must_wait_for_map: pass the epoch rather than the map

have_same_or_newer_map is also modified to accept epoch instead of
map.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
Merge pull request #2071 from somnathr/wip-sd-cpu-optimized

Wip sd cpu optimized

Reviewed-by: Samuel Just <sam.just@inktank.com>