codec: add define constants for RFC5993 and TS101318

The difference between the RFC5993 and the TS101318 format is only that
RFC5993 has one additional ToC (Table of contents) byte at the
beginning. However it can be difficult to remember which of the two
formats has the ToC byte at at the beginning and which hasn't.

Let's add a constant that defines the length for both formats so that we
can make it more clear in the code which format we are refering to.

Related: OS#5688
Change-Id: I125ef9cdab98c073971841c175b1a7dcd927f9c2
diff --git a/include/osmocom/codec/codec.h b/include/osmocom/codec/codec.h
index 364385b..a656bcf 100644
--- a/include/osmocom/codec/codec.h
+++ b/include/osmocom/codec/codec.h
@@ -15,6 +15,10 @@
 /* TS 101318 Chapter 5.3: 244 bits + 4bit sig */
 #define GSM_EFR_BYTES	31
 
+/* Number of bytes of an GSM_HR RTP payload */
+#define GSM_HR_BYTES_RTP_RFC5993 (GSM_HR_BYTES + 1)
+#define GSM_HR_BYTES_RTP_TS101318 (GSM_HR_BYTES)
+
 extern const uint16_t gsm610_bitorder[];	/* FR */
 extern const uint16_t gsm620_unvoiced_bitorder[]; /* HR unvoiced */
 extern const uint16_t gsm620_voiced_bitorder[];   /* HR voiced */