daemon-helper: use _nm_strerror_r() to avoid non-thread-safe strerror()

Yes, there probably are not multiple threads here. It's a matter of principle to
not use smelly functions.

Also, copy the "errno" value we want to print, before calling various functions.

(cherry picked from commit c42f6f0997)

src/nm-daemon-helper/nm-daemon-helper.c

@@ -120,8 +120,8 @@ cmd_resolve_address(void)
                     service,
                     ret,
                     gai_strerror(ret),
-                    errno,
-                    strerror(errno));
+                    errsv,
+                    _nm_strerror_r(errsv, buf, sizeof(buf)));
         } else {
             fprintf(stderr,
                     "getnameinfo() via service '%s' failed: %d (%s)\n",