logging: log to stderr when logging is not initialized

When the logging framework is not initialized we get an error:

"ERROR: osmo_log_info == NULL! You must call log_init() before
using logging in ..."

There are sometimes situations where some code tries to log before
logging was initialied. This is a problem because the actual log
line with the debug info we need is covered up by the error message
from the logging framework.

Lets introduce a fallback logging function that is called when the
the logging framework is not available. This function can just use
fprintf to output to stderr.

Change-Id: I9b1b0988e02322e3e44fd4ceea3e1bc2d4df3c45
diff --git a/src/logging.c b/src/logging.c
index 94d183f..148bb27 100644
--- a/src/logging.c
+++ b/src/logging.c
@@ -754,6 +754,18 @@
 	TRACE(LIBOSMOCORE_LOG_DONE());
 }
 
+/* This logging function is used as a fallback when the logging framework is
+ * not is not properly initialized. */
+void logp_stub(const char *file, int line, int cont, const char *format, ...)
+{
+	va_list ap;
+	if (!cont)
+		fprintf(stderr, "%s:%d ", file, line);
+	va_start(ap, format);
+	vfprintf(stderr, format, ap);
+	va_end(ap);
+}
+
 /*! Register a new log target with the logging core
  *  \param[in] target Log target to be registered
  */