input/lapd.c: Enlarge message buffers for DL-SAP primitives

The DL-SAP primitive msgbs are currently allocated
to only have headroom but no tailroom.  Let's change that

Change-Id: Ia476c8a2f70e6579be53230427923885a573f801
Related: OS#4644
diff --git a/src/input/lapd.c b/src/input/lapd.c
index 9bab5a9..5c0a6b6 100644
--- a/src/input/lapd.c
+++ b/src/input/lapd.c
@@ -82,7 +82,7 @@
 #define LOGSAP(sap, level, fmt, args ...) \
 	LOGP(DLLAPD, level, "%s: " fmt, (sap)->dl.name, ## args)
 
-#define DLSAP_MSGB_SIZE		56
+#define DLSAP_MSGB_SIZE		128
 #define DLSAP_MSGB_HEADROOM	56
 
 const struct lapd_profile lapd_profile_isdn = {