svcrdma: trace cc_release calls

This event brackets the svcrdma_post_* trace points. If this trace
event is enabled but does not appear as expected, that indicates a
chunk_ctxt leak.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Tom Talpey <tom@talpey.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>