xsk: add id to umem

This commit adds an id to the umem structure. The id uniquely
identifies a umem instance, and will be exposed to user-space via the
socket monitoring interface.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/net/xdp_sock.h

@@ -42,6 +42,7 @@ struct xdp_umem {
 	struct work_struct work;
 	struct page **pgs;
 	u32 npgs;
+	int id;
 	struct net_device *dev;
 	struct xdp_umem_fq_reuse *fq_reuse;
 	u16 queue_id;