selftests/bpf: Fix kfree_skb on s390x

h_proto is big-endian; use htons() in order to make comparison work on
both little- and big-endian machines.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230128000650.1516334-7-iii@linux.ibm.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>