eth: fbnic: fix missing programming of the default descriptor

eth: fbnic: fix missing programming of the default descriptor

XDP_TX typically uses no offloads. To optimize XDP we added a "default
descriptor" feature to the chip, which allows us to send XDP frames with
just the buffer descriptors (DMA address + length). All the metadata
descriptors are derived from the queue config.

Commit under Fixes missed adding setting the defaults up when transplanting
the code from the prototype driver. Importantly after reset the "request
completion" bit is not set. Packets still get sent but there's no
completion, so ring is not cleaned up. We can send one ring's worth
of packets and then will start dropping all frames that got the XDP_TX
action from the XDP prog.

Reviewed-by: Simon Horman <horms@kernel.org>
Fixes: 168deb7b31b2 ("eth: fbnic: Add support for XDP_TX action")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20251007232653.2099376-2-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>