strrb: Add missing #include to talloc.h

The strrb.c code uses talloc API without using the proper #include.

Change-Id: I4ac485324f40545339d8df6884f1dea319a23648
diff --git a/src/strrb.c b/src/strrb.c
index 8f925bd..069a699 100644
--- a/src/strrb.c
+++ b/src/strrb.c
@@ -30,6 +30,7 @@
 #include <string.h>
 
 #include <osmocom/core/strrb.h>
+#include <osmocom/core/talloc.h>
 
 /* Ringbuffer assumptions, invarients, and notes:
  * - start is the index of the first used index slot in the ring buffer.