tbf: Do not kill DL TBF on Packet Resource Request

Currently all active TBF of an MS are killed if a Packet Resource
Request is received from the MS. In general this happens after a RACH
request. This does not happen after a resource request that has been
included into a Downlink Ack/Nack.

Sometimes an UL TBF is requested by an MS via RACH while a DL TBF is
running for instance to send a TCP Ack. This can happen, if a former
request via PACCH did not work.

This commit removes the killing of the DL TBF from
gprs_rlcmac_pdch::rcv_resource_request().

Sponsored-by: On-Waves ehf
diff --git a/tests/tbf/TbfTest.cpp b/tests/tbf/TbfTest.cpp
index 44d26b2..6f9a8ba 100644
--- a/tests/tbf/TbfTest.cpp
+++ b/tests/tbf/TbfTest.cpp
@@ -871,11 +871,11 @@
 	OSMO_ASSERT(ms2 == ms);
 
 	/* DL TBF should be the same */
-	/* OSMO_ASSERT(ms->dl_tbf()); */
-	/* OSMO_ASSERT(ms->dl_tbf() == dl_tbf); */
+	OSMO_ASSERT(ms->dl_tbf());
+	OSMO_ASSERT(ms->dl_tbf() == dl_tbf);
 
 	/* No queued packets should be lost */
-	/* OSMO_ASSERT(ms->llc_queue()->size() == 1); */
+	OSMO_ASSERT(ms->llc_queue()->size() == 1);
 
 	printf("=== end %s ===\n", __func__);
 }