interfaces: add udev netlink support to hardware-observe
With the addition of seccomp argument filtering the socket syscall will not allow NETLINK_KOBJECT_UEVENT anymore. But this is crucial for the hardware-observe interface to monitor udev. This patch adds it back.
As part of the investigation for the livepatch regression and netlink socket mediation, net/core/* from the Linux kernel sources shows that the kernel is using kobject_uevent() for notifications. While we could force snaps to use hardware-observe to view these, it makes sense in terms of completeness for these interfaces and for compatibility with existing snaps to allow 'socket AF_NETLINK - NETLINK_KOBJECT_UEVENT' here as well.