net: mana: Add RX fencing

RX fencing allows the driver to know that any prior change to the RQs has
finished, e.g. when the RQs are disabled/enabled or the hashkey/indirection
table are changed, RX fencing is required.

Remove the previous workaround "ssleep(1)" and add the real support for
RX fencing as the PF driver supports the MANA_FENCE_RQ request now (any
old PF driver not supporting the request won't be used in production).

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Link: https://lore.kernel.org/r/20211216001748.8751-1-decui@microsoft.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>