selftests/xsk: Avoid bpf_link probe for existing xsk

Currently bpf_link probe is done for each call of xsk_socket__create().
For cases where xsk context was previously created and current socket
creation uses it, has_bpf_link will be overwritten, where it has already
been initialized.

Optimize this by moving the query to the xsk_create_ctx() so that when
xsk_get_ctx() finds a ctx then no further bpf_link probes are needed.
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20220629143458.934337-2-maciej.fijalkowski@intel.com

tools/testing/selftests/bpf/xsk.c

@@ -958,6 +958,7 @@ static struct xsk_ctx *xsk_create_ctx(struct xsk_socket *xsk,
 	ctx->fill = fill;
 	ctx->comp = comp;
 	list_add(&ctx->list, &umem->ctx_list);
+	ctx->has_bpf_link = xsk_probe_bpf_link();
 	return ctx;
 }
 
@@ -1059,7 +1060,6 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 		}
 	}
 	xsk->ctx = ctx;
-	xsk->ctx->has_bpf_link = xsk_probe_bpf_link();
 
 	if (rx && !rx_setup_done) {
 		err = setsockopt(xsk->fd, SOL_XDP, XDP_RX_RING,