ip_tunnels, bpf: define IP_TUNNEL_OPTS_MAX and use it

eBPF defines this as BPF_TUNLEN_MAX and OVS just uses the hard-coded
value inside struct sw_flow_key. Thus, add and use IP_TUNNEL_OPTS_MAX
for this, which makes the code a bit more generic and allows to remove
BPF_TUNLEN_MAX from eBPF code.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/openvswitch/flow.h b/net/openvswitch/flow.h
index 1d055c5..03378e7 100644
--- a/net/openvswitch/flow.h
+++ b/net/openvswitch/flow.h
@@ -55,7 +55,7 @@
 	FIELD_SIZEOF(struct sw_flow_key, recirc_id))
 
 struct sw_flow_key {
-	u8 tun_opts[255];
+	u8 tun_opts[IP_TUNNEL_OPTS_MAX];
 	u8 tun_opts_len;
 	struct ip_tunnel_key tun_key;	/* Encapsulating tunnel key. */
 	struct {