OC-2G: Fix missing header

From-Commit: a9eefb54c62a
From-Remote: https://gitlab.com/nrw_noa/osmo-pcu
Change-Id: Ida0592c9da74588a57d9d2d5be40fcf79edcb596
diff --git a/src/osmo-bts-oc2g/oc2g_l1_if.c b/src/osmo-bts-oc2g/oc2g_l1_if.c
index 23661cb..3855da1 100644
--- a/src/osmo-bts-oc2g/oc2g_l1_if.c
+++ b/src/osmo-bts-oc2g/oc2g_l1_if.c
@@ -31,6 +31,8 @@
 #include <osmocom/core/gsmtap.h>
 #include <osmocom/core/talloc.h>
 #include <osmocom/core/timer.h>
+#include <osmocom/gsm/protocol/gsm_04_08.h>
+
 #include <gprs_debug.h>
 #include <pcu_l1_if.h>
 #include <osmocom/pcu/pcuif_proto.h>