backtrace: use namespace prefix osmo_*

Summary of changes:

s/backtrace/osmo_backtrace/g
diff --git a/src/backtrace.c b/src/backtrace.c
index ecd6b9c..8281fad 100644
--- a/src/backtrace.c
+++ b/src/backtrace.c
@@ -29,7 +29,7 @@
 
 #ifdef HAVE_EXECINFO_H
 #include <execinfo.h>
-void generate_backtrace()
+void osmo_generate_backtrace()
 {
 	int i, nptrs;
 	void *buffer[100];