tbf: Move the LLC queue to GprsMs

Currently the enqueued DL LLC messages which have not yet passed to
RLC/MAC encoding are eventually copied from one TBF to the next one
(see gprs_rlcmac_dl_tbf::reuse_tbf). Since the enqueued LLC messages
are related to a specific MS, they should be stored at that layer.

This commit moves the gprs_llc_queue object to GprsMs and changes the
TBF's accessor methods accordingly. The LLC copying code is removed
from gprs_rlcmac_dl_tbf::reuse_tbf().

Sponsored-by: On-Waves ehf
diff --git a/src/gprs_ms.cpp b/src/gprs_ms.cpp
index f5b92d2..d047cf5 100644
--- a/src/gprs_ms.cpp
+++ b/src/gprs_ms.cpp
@@ -81,6 +81,7 @@
 	m_imsi[0] = 0;
 	memset(&m_timer, 0, sizeof(m_timer));
 	m_timer.cb = GprsMs::timeout;
+	m_llc_queue.init();
 }
 
 GprsMs::~GprsMs()
@@ -99,6 +100,7 @@
 		m_dl_tbf->set_ms(NULL);
 		m_dl_tbf = NULL;
 	}
+	m_llc_queue.clear(NULL);
 }
 
 void* GprsMs::operator new(size_t size)