We calculate guest offloads during probe without the protection of
rtnl_lock. This lead to race between probe and ndo_set_features. Fix
this by moving the calculation under the rtnl_lock.

Fixes: 3f93522f ("virtio-net: switch off offloads on demand if possible on XDP set")
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://patch.msgid.link/20240814052228.4654-5-jasowang@redhat.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>