[SBI] Make 'global' configuration optional instead of mandatory (#3466)

Previously, the global configuration section was required for NF to start,
which differed from earlier versions where it was optional. This commit modifies
the implementation to make the global section optional again,
allowing NF to start without explicitly defining global settings.

This change restores the previous behavior and improves usability for users
who do not need to customize global settings.

lib/core/ogs-epoll.c

@@ -75,7 +75,8 @@ static void epoll_init(ogs_pollset_t *pollset)
 
     context->epfd = epoll_create(pollset->capacity);
     if (context->epfd < 0) {
-        ogs_log_message(OGS_LOG_FATAL, ogs_errno, "epoll_create() failed");
+        ogs_log_message(OGS_LOG_FATAL, ogs_errno,
+                "epoll_create() failed [%d]", pollset->capacity);
         ogs_assert_if_reached();
         return;
     }