migration/rdma: Don't use imaginary transfers

RDMA protocol is completely asynchronous, so in qemu_rdma_save_page()
they "invent" that a byte has been transferred.  And then they call
qemu_file_credit_transfer() and ram_transferred_add() with that byte.
Just remove that calls as nothing has been sent.

Reviewed-by: Leonardo Bras <leobras@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-Id: <20230515195709.63843-14-quintela@redhat.com>