gsm_rlcmac: Enhance dissection of PSI1

Port of wireshark.git 7e9411fee3a101b53693210f7a38789fd4c70ba2.

Ported-by: Pau Espin Pedrol <pespin@sysmocom.de>
Change-Id: I89d488c1f349c556e40a9d13895b1309d5140212
diff --git a/src/gsm_rlcmac.h b/src/gsm_rlcmac.h
index 90c5bfd..b05483c 100644
--- a/src/gsm_rlcmac.h
+++ b/src/gsm_rlcmac.h
@@ -2492,9 +2492,16 @@
 
 typedef struct
 {
-  guint8 MSCR;
-  guint8 SGSNR;
-  guint8 BandIndicator;
+  guint8 LB_MS_TXPWR_MAX_CCH;
+} PSI1_AdditionsR6_t;
+
+typedef struct
+{
+  guint8             MSCR;
+  guint8             SGSNR;
+  guint8             BandIndicator;
+  gboolean           Exist_AdditionsR6;
+  PSI1_AdditionsR6_t AdditionsR6;
 } PSI1_AdditionsR99_t;
 
 typedef struct