client: don't embed cap releases in clientreplay

If the client is sending replay requests, avoid sending embedded caps,
since the mds already has the client's caps from the reconnect.
This matches the behavior of the kernel client.

Fixes #4742.
Signed-off-by: Sam Lang <sam.lang@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
Reviewed-by: Greg Farnum <greg@inktank.com>