MINOR: cfgparse: make the process/thread parser support a maximum value

It was hard-wired to LONGBITS, let's make it configurable depending on the
context (threads, processes).
diff --git a/src/cfgparse-listen.c b/src/cfgparse-listen.c
index 2a7ed53..74218b5 100644
--- a/src/cfgparse-listen.c
+++ b/src/cfgparse-listen.c
@@ -922,7 +922,7 @@
 				set = 0;
 				break;
 			}
-			if (parse_process_number(args[cur_arg], &set, NULL, &errmsg)) {
+			if (parse_process_number(args[cur_arg], &set, LONGBITS, NULL, &errmsg)) {
 				ha_alert("parsing [%s:%d] : %s : %s\n", file, linenum, args[0], errmsg);
 				err_code |= ERR_ALERT | ERR_FATAL;
 				goto out;