net: filter: add test case for jump with holes and ret x variants

This patch adds three more test cases:

 1) long jumps with holes of unreachable code
 2) ret x
 3) ldx + ret x

All three tests are for classical BPF and to make sure that
any changes will not break some exotic behaviour that exists
probably since decades. The last two tests are expected to
fail by the BPF checker already, as in classic BPF only K
or A are allowed to be returned. Thus, there are now 52 test
cases for BPF.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>