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_sched.cpp b/src/gprs_rlcmac_sched.cpp
index 37e8d38..40a183b 100644
--- a/src/gprs_rlcmac_sched.cpp
+++ b/src/gprs_rlcmac_sched.cpp
@@ -95,7 +95,7 @@
 			continue;
 
 		/* use this USF */
-		usf = tbf->dir.ul.usf[ts];
+		usf = tbf->m_usf[ts];
 		LOGP(DRLCMACSCHED, LOGL_DEBUG, "Received RTS for PDCH: TRX=%d "
 			"TS=%d FN=%d block_nr=%d scheduling USF=%d for "
 			"required uplink resource of UL TFI=%d\n", trx, ts, fn,
@@ -186,7 +186,7 @@
 			continue;
 
 		/* waiting for CCCH IMM.ASS confirm */
-		if (tbf->dir.dl.wait_confirm)
+		if (tbf->m_wait_confirm)
 			continue;
 
 		LOGP(DRLCMACSCHED, LOGL_DEBUG, "Scheduling data message at "