gsm_04_14: fix off-by-one error in create_gsm0414_msg()

This byte is redundant, and must not be allocated in this function.
A consequence of this error is that the MS alwats interprets the
"Sub-channel" IE as test loop A regardless of the specified type.

Here is an example of malformed Close TCH loop (type C) message:

  0f 00 00 04
  x. .. .. ..  - Skip indicator (see 3GPP TS 24.007)
  .x .. .. ..  - Protocol discriminator (see 3GPP TS 24.007)
  .. xx .. ..  - Message type (CLOSE_TCH_LOOP_CMD)
  .. .. !! ..  - (!) Redundant byte from create_gsm0414_msg()
  .. .. .. xx  - (!) The actual "Sub-channel" IE (loop C, X=0)

Change-Id: Ia47225b884439dcd43be307e7351994e55fcd50d

src/libmsc/gsm_04_14.c

@@ -43,7 +43,7 @@ static struct msgb *create_gsm0414_msg(uint8_t msg_type)
 	struct msgb *msg = gsm48_msgb_alloc_name("GSM 04.14");
 	struct gsm48_hdr *gh;
 
-	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh) + 1);
+	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
 	gh->proto_discr = GSM48_PDISC_TEST;
 	gh->msg_type = msg_type;
 	return msg;