tree-wide: clean up log_syntax() usage

- Rely everywhere that we use abs() on the error code passed in anyway,
  thus don't need to explicitly negate what we pass in

- Never attach synthetic error number information to log messages. Only
  log about errors we *receive* with the error number we got there,
  don't log any synthetic error, that don#t even propagate, but just eat
  up.

- Be more careful with attaching exactly the error we get, instead of
  errno or unrelated errors randomly.

- Fix one occasion where the error number and line number got swapped.

- Make sure we never tape over OOM issues, or inability to resolve
  specifiers

src/resolve/resolved-conf.c

@@ -95,7 +95,7 @@ int config_parse_dnsv(
                 /* Otherwise add to the list */
                 r = manager_parse_dns_server(m, ltype, rvalue);
                 if (r < 0) {
-                        log_syntax(unit, LOG_ERR, filename, line, -r, "Failed to parse DNS server string '%s'. Ignoring.", rvalue);
+                        log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse DNS server string '%s'. Ignoring.", rvalue);
                         return 0;
                 }
         }
@@ -131,7 +131,7 @@ int config_parse_support(
         if (support < 0) {
                 r = parse_boolean(rvalue);
                 if (r < 0) {
-                        log_syntax(unit, LOG_ERR, filename, line, -r, "Failed to parse support level '%s'. Ignoring.", rvalue);
+                        log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse support level '%s'. Ignoring.", rvalue);
                         return 0;
                 }