misc: Add prototypes to header files, include more header files

Fix various warnings about implicit declarations of functions.
diff --git a/openbsc/src/db.c b/openbsc/src/db.c
index 51f94b6..0bb86fe 100644
--- a/openbsc/src/db.c
+++ b/openbsc/src/db.c
@@ -21,6 +21,7 @@
  */
 
 #include <openbsc/gsm_data.h>
+#include <openbsc/gsm_04_11.h>
 #include <openbsc/db.h>
 #include <openbsc/talloc.h>