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
96a8eb1e ("bpf: fix samples to add fake KBUILD_MODNAME").

Fixes: 12d8bb64 ("bpf: xdp: Add XDP example for head adjustment")
Fixes: 90e02896 ("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>