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/tbf_dl.cpp b/src/tbf_dl.cpp
index b350720..1dd7dd8 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -145,7 +145,7 @@
 	}
 
 	// Create new TBF (any TRX)
-#warning "Copy and paste with alloc_ul_tbf"
+/* FIXME: Copy and paste with alloc_ul_tbf */
 	/* set number of downlink slots according to multislot class */
 	dl_tbf = tbf_alloc_dl_tbf(bts, ms, use_trx, ms_class, egprs_ms_class, ss);