hash map is unordered, so get_next_key() iterator shouldn't
rely on particular order of elements. So relax this test.

Fixes: ffb65f27 ("bpf: add a testsuite for eBPF maps")
Reported-by: NMichael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: NAlexei Starovoitov <ast@plumgrid.com>
Acked-by: NDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>