NX may be processing requests while trying to close window. Wait until
all credits are returned and then free send window from VAS instance.
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1587017256.2275.1076.camel@hbabu-laptop