tools: bpf_jit_disasm: fix segfault on disabled debugging log output

With recent debugging, I noticed that bpf_jit_disasm segfaults when
there's no debugging output from the JIT compiler to the kernel log.

Reason is that when regexec(3) doesn't match on anything, start/end
offsets are not being filled out and contain some uninitialized garbage
from stack. Thus, we need zero out offsets first.

Signed-off-by: Daniel Borkmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/net/bpf_jit_disasm.c

···
 	assert(ret == 0);
 
 	ptr = haystack;
+	memset(pmatch, 0, sizeof(pmatch));
+
 	while (1) {
 		ret = regexec(&regex, ptr, 1, pmatch, 0);
 		if (ret == 0) {