daemon: enable multithread logging in main()

It may happen that multiple threads trying to log at the same time,
and the msgb containing a logging message gets corrupted in
libosmocore's _file_wq_write_cb():

  msgb(0x7f5ca2a38150): msgb too small to pull 240 (len 120)
  Aborted (core dumped)

'''
  rc = write(ofd->fd, msgb_data(msg), msgb_length(msg));
  if (rc < 0)
      return rc;
  if (rc != msgb_length(msg)) { // 240 != 120
      /* pull the number of bytes we have already written */
      msgb_pull(msg, rc); // <-- we abort() here
      /* ask write_queue to re-insert the msgb at the head of the queue */
      return -EAGAIN;
  }
'''

The return value of write() cannot be greater than the given length.
Most likely, the msgb gets corrupted during the write() system call.

Enabling multithread logging in libosmocore solves the problem.

Change-Id: Ib14d0e36e8cd72465bfe55d19b68dbe3423f7f05
Related: SYS#5602
Fixes: OS#5424
diff --git a/daemon/main.c b/daemon/main.c
index fec6f84..788ed70 100644
--- a/daemon/main.c
+++ b/daemon/main.c
@@ -726,6 +726,7 @@
 
 	osmo_init_ignore_signals();
 	osmo_init_logging2(g_tall_ctx,  &log_info);
+	log_enable_multithread();
 
 	g_daemon = gtp_daemon_alloc(g_tall_ctx);
 	OSMO_ASSERT(g_daemon);