encoding: Use MT_PACKET_UPLINK_ASSIGNMENT define instead of hardcoded value

Change-Id: I05b39d3183fdf741d648a15ff803d20e324443af
diff --git a/src/encoding.cpp b/src/encoding.cpp
index 278da72..74b80c1 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -605,7 +605,7 @@
 
 	/* See 3GPP TS 44.060, section 11.2.29 */
 	pua = &block->u.Packet_Uplink_Assignment;
-	pua->MESSAGE_TYPE = 0x0a;  // Packet Uplink Assignment
+	pua->MESSAGE_TYPE = MT_PACKET_UPLINK_ASSIGNMENT;  // Packet Uplink Assignment
 	pua->PAGE_MODE    = 0x00;  // Normal Paging
 
 	/* TLLI or Global (UL/DL) TFI */