eth: fbnic: Advertise supported XDP features.

Drivers are supposed to advertise the XDP features they support. This was
missed while adding XDP support.

Before:
$ ynl --family netdev --dump dev-get
...
{'ifindex': 3,
'xdp-features': set(),
'xdp-rx-metadata-features': set(),
'xsk-features': set()},
...

After:
$ ynl --family netdev --dump dev-get
...
{'ifindex': 3,
'xdp-features': {'basic', 'rx-sg'},
'xdp-rx-metadata-features': set(),
'xsk-features': set()},
...

Fixes: 168deb7b31b2 ("eth: fbnic: Add support for XDP_TX action")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Dimitri Daskalakis <dimitri.daskalakis1@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260218030620.3329608-1-dimitri.daskalakis1@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>