tbf, ...: Make the fields in the dl/ul struct member variables

There is no need for the union/struct anymore. Make the variable members
of the UL/DL class.

As a result gprs_rlc_dl_window gets a reset() method because
memset(&dir.dl, 0, sizeof(dir.dl)) doesn't work anymore in reuse_tbf().

Ticket: SYS#389
Sponsored by: On-Waves ehf
diff --git a/src/gprs_rlcmac_ts_alloc.cpp b/src/gprs_rlcmac_ts_alloc.cpp
index 038d1fe..27b01d7 100644
--- a/src/gprs_rlcmac_ts_alloc.cpp
+++ b/src/gprs_rlcmac_ts_alloc.cpp
@@ -86,7 +86,7 @@
 		tbf = pdch->ul_tbf_by_tfi(tfi);
 		if (!tbf)
 			continue;
-		usf_map |= (1 << tbf->dir.ul.usf[pdch->ts_no]);
+		usf_map |= (1 << tbf->m_usf[pdch->ts_no]);
 	}
 
 	/* look for USF, don't use USF=7 */
@@ -122,7 +122,7 @@
 {
 	tbf->trx->ul_tbf[tbf->tfi()] = tbf;
 	tbf->pdch[pdch->ts_no] = pdch;
-	tbf->dir.ul.usf[pdch->ts_no] = usf;
+	tbf->m_usf[pdch->ts_no] = usf;
 }
 
 static void assign_dlink_tbf(