routing: Fix incorrect detection of Linux slave devices
routing: Fix incorrect detection of Linux slave devices

Using method Slave() exposed by the netlink package doesn't always work.
In particular, it doesn't work on AKS, maybe because there's no master
bond interface in that case. We should instead rely on the flags passed
by Linux's netlink API.

Fixes: 3e245517 ("routing: Fix incorrect interface selection for pod routes")
Signed-off-by: Paul Chaignon <a027184a55211cd23e3f3094f1fdc728df5e0500@cilium.io>

cilium/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,tklauser/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium