Handle packet access reject during packet resource request

When Packet resource request is received, PCU will generate the
packet access reject if no resources are present. The encoding is done
based on section 7.1.3.2.1 and 8.1.2.5 of 44.060 version 7.27.0 Release 7.
This patch also includes the test case to validate the generated
packet access reject message.

This patch is integration tested on Osmo-trx setup with Ettus B210 board
and LG F70 MS with some simulation code changes in Osmo-pcu.

Change-Id: I05ff25124b58905586caa0c0c37023d69724f121
diff --git a/tests/tbf/TbfTest.ok b/tests/tbf/TbfTest.ok
index d531437..077ec4e 100644
--- a/tests/tbf/TbfTest.ok
+++ b/tests/tbf/TbfTest.ok
@@ -77,3 +77,7 @@
 === start test_packet_access_rej_epdan ===
 packet reject: 40 84 7f f7 6e e6 41 4b 2b 2b 2b 2b 2b 2b 2b 2b 2b 2b 2b 2b 2b 2b 2b 
 === end test_packet_access_rej_epdan ===
+=== start test_packet_access_rej_prr ===
+=== end test_packet_access_rej_prr ===
+=== start test_packet_access_rej_prr_no_other_tbfs ===
+=== end test_packet_access_rej_prr_no_other_tbfs ===