bpf: fix samples xdp_tx_iptunnel and tc_l2_redirect with fake KBUILD_MODNAME

Fix build errors for samples/bpf xdp_tx_iptunnel and tc_l2_redirect,
when dynamic debugging is enabled (CONFIG_DYNAMIC_DEBUG) by defining a
fake KBUILD_MODNAME.

Just like Daniel Borkmann fixed other samples/bpf in commit
96a8eb1eee ("bpf: fix samples to add fake KBUILD_MODNAME").

Fixes: 12d8bb64e3 ("bpf: xdp: Add XDP example for head adjustment")
Fixes: 90e02896f1 ("bpf: Add test for bpf_redirect to ipip/ip6tnl")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

samples/bpf/tc_l2_redirect_kern.c

@@ -4,6 +4,7 @@
  * modify it under the terms of version 2 of the GNU General Public
  * License as published by the Free Software Foundation.
  */
+#define KBUILD_MODNAME "foo"
 #include <uapi/linux/bpf.h>
 #include <uapi/linux/if_ether.h>
 #include <uapi/linux/if_packet.h>

samples/bpf/xdp_tx_iptunnel_kern.c

@@ -8,6 +8,7 @@
  * encapsulating the incoming packet in an IPv4/v6 header
  * and then XDP_TX it out.
  */
+#define KBUILD_MODNAME "foo"
 #include <uapi/linux/bpf.h>
 #include <linux/in.h>
 #include <linux/if_ether.h>