switch to libosmocore multihread-logging

When osmo-remsim was originally developed, libosmocore logging was
not yet thread-safe.  This meant that the worker threads of remsim-bankd
and remsim-server could not log via the libosmocore logging framework
but directly used stderr/stdout, which produced rather inconsistent log
output.

However, since 1.3.0, libosmocore has received support for
multi-threaded applications.  Let's make use of this and consistently
use it in remsim-server and remsim-bankd.  This obviously also means
adding some more log categories.

Change-Id: I7bd5264c559b756927046563a2d00c54826bee9b
diff --git a/src/server/rspro_server.c b/src/server/rspro_server.c
index b35800f..6514f80 100644
--- a/src/server/rspro_server.c
+++ b/src/server/rspro_server.c
@@ -709,11 +709,11 @@
 	/* read from the socket to "confirm" the event and make it non-readable again */
 	rc = read(ofd->fd, &value, 8);
 	if (rc < 8) {
-		fprintf(stderr, "Error reading eventfd: %d\n", rc);
+		LOGP(DMAIN, LOGL_ERROR, "Error reading eventfd: %d\n", rc);
 		return rc;
 	}
 
-	printf("rspro_server: Event FD arrived, checking for any pending work\n");
+	LOGP(DMAIN, LOGL_INFO, "Event FD arrived, checking for any pending work\n");
 
 	pthread_rwlock_rdlock(&srv->rwlock);
 	llist_for_each_entry(conn, &srv->banks, list) {