Mark several fsm related internal symbols as static

After some earlier refactoring, those fields are only used internally in
the module, and hence can be marked as static.

Change-Id: Ibf2a6ee5636ae7102ffd13b7497769652bcc3202
diff --git a/src/tbf_dl_fsm.c b/src/tbf_dl_fsm.c
index 6b455da..a0b1c03 100644
--- a/src/tbf_dl_fsm.c
+++ b/src/tbf_dl_fsm.c
@@ -29,7 +29,7 @@
 
 #define X(s) (1 << (s))
 
-const struct osmo_tdef_state_timeout tbf_dl_fsm_timeouts[32] = {
+static const struct osmo_tdef_state_timeout tbf_dl_fsm_timeouts[32] = {
 	[TBF_ST_NEW] = {},
 	[TBF_ST_ASSIGN] = { },
 	[TBF_ST_FLOW] = { },