Add new tests samples/bpf/test_verifier:

unpriv: return pointer
  checks that pointer cannot be returned from the eBPF program

unpriv: add const to pointer
unpriv: add pointer to pointer
unpriv: neg pointer
  checks that pointer arithmetic is disallowed

unpriv: cmp pointer with const
unpriv: cmp pointer with pointer
  checks that comparison of pointers is disallowed
  Only one case allowed 'void *value = bpf_map_lookup_elem(..); if (value == 0) ...'

unpriv: check that printk is disallowed
  since bpf_trace_printk is not available to unprivileged

unpriv: pass pointer to helper function
  checks that pointers cannot be passed to functions that expect integers
  If function expects a pointer the verifier allows only that type of pointer.
  Like 1st argument of bpf_map_lookup_elem() must be pointer to map.
  (applies to non-root as well)

unpriv: indirectly pass pointer on stack to helper function
  checks that pointer stored into stack cannot be used as part of key
  pass...