osd: change src_oid encoding -- FLAG DAY

osd: change src_oid encoding -- FLAG DAY

The old encoding was mutually exclusive with putting any data payload on
the operation.  That was stupid.. we can't, for example, do xattr ops then
on a src_oid.

Fix this by just including the oid in the data payload inline whenever the
bit is set in the op code.  This changes the client protocol in an
incompatible way, which means users of the CLONERANGE operation need to be
upgrade/downgraded in unison.

Signed-off-by: Sage Weil <sage@newdream.net>