bts: Rename mslot_class_from_ra

This function is actually returning an EGPRS multislot class, so let's
update naming. The variable using the return value was already being
passed as egprs_ms_class to tbf_alloc_ul_tbf().

Change-Id: Idb51836c8c9dd4e865bf2cb0b0c24155662f2ae8
diff --git a/src/bts.cpp b/src/bts.cpp
index 5e1725c..8edde23 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -664,12 +664,21 @@
 	return fn;
 }
 
-static inline uint16_t mslot_class_from_ra(uint16_t ra, bool is_11bit)
+/* 3GPP TS 44.060:
+ *   Table 11.2.5.3: PACKET CHANNEL REQUEST
+ *   Table 11.2.5a.3: EGPRS PACKET CHANNEL REQUEST
+ * Both GPRS and EGPRS use same MultislotClass coding, but since use of PCCCH is
+ * deprecated, no PACKET CHANNEL REQUEST exists, which means for GPRS we will
+ * receive CCCH RACH which doesn't contain any mslot class. Hence in the end we
+ * can only receive EGPRS mslot class through 11-bit EGPRS PACKET CHANNEL
+ * REQUEST.
+ */
+static inline uint16_t egprs_mslot_class_from_ra(uint16_t ra, bool is_11bit)
 {
 	if (is_11bit)
 		return (ra & 0x3e0) >> 5;
 
-	/* set multislot class to 0 for 8-bit RACH, since we don't know it yet */
+	/* set EGPRS multislot class to 0 for 8-bit RACH, since we don't know it yet */
 	return 0;
 }
 
@@ -741,7 +750,7 @@
 	int plen;
 	uint8_t usf = 7;
 	uint8_t tsc = 0, ta = qta2ta(qta);
-	uint16_t ms_class = mslot_class_from_ra(ra, is_11bit);
+	uint16_t egprs_ms_class = egprs_mslot_class_from_ra(ra, is_11bit);
 	bool failure = false;
 
 	rach_frame();
@@ -784,8 +793,7 @@
 	} else {
 		// Create new TBF
 		/* FIXME: Copy and paste with other routines.. */
-
-		tbf = tbf_alloc_ul_tbf(&m_bts, NULL, -1, 0, ms_class, true);
+		tbf = tbf_alloc_ul_tbf(&m_bts, NULL, -1, 0, egprs_ms_class, true);
 
 		if (!tbf) {
 			LOGP(DRLCMAC, LOGL_NOTICE, "No PDCH resource sending "