vlr_auth_fsm.h/vlr_sgs_fsm.h: forward declare struct vlr_subscr

Make the headers self-contained to not depend on the include order.

Change-Id: I0985b60ed252c37663b945eed939519d17c4c985
diff --git a/src/libvlr/vlr_auth_fsm.h b/src/libvlr/vlr_auth_fsm.h
index 8283842..441a8ca 100644
--- a/src/libvlr/vlr_auth_fsm.h
+++ b/src/libvlr/vlr_auth_fsm.h
@@ -2,6 +2,8 @@
 
 #include <osmocom/core/utils.h>
 
+struct vlr_subscr;
+
 /* Parameters to VLR_AUTH_E_MS_AUTH_RESP */
 struct vlr_auth_resp_par {
 	bool is_r99;
diff --git a/src/libvlr/vlr_sgs_fsm.h b/src/libvlr/vlr_sgs_fsm.h
index 94f202b..6a09433 100644
--- a/src/libvlr/vlr_sgs_fsm.h
+++ b/src/libvlr/vlr_sgs_fsm.h
@@ -20,6 +20,8 @@
 
 #pragma once
 
+struct vlr_subscr;
+
 enum sgs_ue_fsm_event {
 	SGS_UE_E_VLR_FAILURE,
 	SGS_UE_E_RX_RESET_FROM_MME,