net/mlx5: support Rx queue delay drop

net/mlx5: support Rx queue delay drop

For the Ethernet RQs, if there all receiving descriptors are
exhausted, the packets being received will be dropped. This behavior
prevents slow or malicious software entities at the host from
affecting the network. While for hairpin cases, even if there is no
software involved during the packet forwarding from Rx to Tx side,
some hiccup in the hardware or back pressure from Tx side may still
cause the descriptors to be exhausted. In certain scenarios it may be
preferred to configure the device to avoid such packet drops,
assuming the posting of descriptors will resume shortly.

To support this, a new devarg "delay_drop" is introduced. By default,
the delay drop is enabled for hairpin Rx queues and disabled for
standard Rx queues. This value is used as a bit mask:
  - bit 0: enablement of standard Rx queue
  - bit 1: enablement of hairpin Rx queue
And this attribute will be applied to all Rx queues of a device.

The "rq_delay_drop" capability in the HCA_CAP is checked before
creating any queue. If the hardware capabilities do not support
this delay drop, all the Rx queues will still be created without
this attribute, and the devarg setting will be ignored even if it
is specified explicitly. A warning log is used to notify the
application when this occurs.

Signed-off-by: Bing Zhao <bingz@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>