MINOR: tcpcheck: Reject unknown keyword during parsing of healthcheck section

unknown keyword was just ignored. it is not really handy to detect
error. Now an error is reported and the parsing is aborted.

src/tcpcheck.c

@@ -5905,6 +5905,10 @@ int cfg_parse_healthchecks(const char *file, int linenum, char **args, int kwm)
 		}
 		goto out;
 	}
+	else {
+		ha_alert("parsing [%s:%d] : unknown keyword '%s' in '%s' section\n", file, linenum, args[0], cursection);
+		err_code |= ERR_ALERT | ERR_ABORT;
+	}
 
   out:
 	free(errmsg);