cosmetic: convert explicit warnings to fixme/todo

We do not use this style (#warning as an issue tracker replacement) in
any other Osmocom project. Also those warnings clutter compiler output
making it harder to spot warnings for the actual code.

Change-Id: I72070e2a027e60e8b80c12ccfa23ff075434689f
diff --git a/src/bts.cpp b/src/bts.cpp
index add6ab3..b768569 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -649,7 +649,7 @@
 		}
 	} else {
 		// Create new TBF
-		#warning "Copy and paste with other routines.."
+		/* FIXME: Copy and paste with other routines.. */
 
 		if (is_11bit) {
 			tbf = tbf_alloc_ul_tbf(&m_bts, NULL, -1, 0,