argdist: Generated streq-helper to ignore null terminator

Oftentimes we want to use the STRCMP helper to compare strings that
are not null-terminated, e.g. in USDT probes this often happens.
Ignore the null terminator (i.e. loop until the last character
excluding the null terminator).

tools/argdist.py

@@ -258,7 +258,7 @@ def _generate_streq_function(self, string):
  char needle[] = %s;
  char haystack[sizeof(needle)];
  bpf_probe_read(&haystack, sizeof(haystack), (void *)str);
- for (int i = 0; i < sizeof(needle); ++i) {
+ for (int i = 0; i < sizeof(needle)-1; ++i) {
  if (needle[i] != haystack[i]) {
  return false;
  }