Replace tbf->establish_dl_tbf_on_pacch() refactoring GprsMs functions

ms_new_dl_tbf_assignment() is split into 2 functions, one to
allocate+assign on PACCH and another one for PCH.
This makes a lot clearer the aim of each caller of the function.
Once this is done, it becomes obvious tbf->establish_dl_tbf_on_pacch()
is basically doing the same as ms_new_dl_tbf_assigned_on_pacch() so drop
it.

Change-Id: I610210e3120c962d91ce8ff94c66161e086761ba
diff --git a/src/gprs_ms.h b/src/gprs_ms.h
index b9a1386..8014f26 100644
--- a/src/gprs_ms.h
+++ b/src/gprs_ms.h
@@ -144,7 +144,8 @@
 bool ms_nacc_rts(const struct GprsMs *ms);
 struct msgb *ms_nacc_create_rlcmac_msg(struct GprsMs *ms, struct gprs_rlcmac_tbf *tbf, uint32_t fn, uint8_t ts);
 
-int ms_new_dl_tbf_assignment(struct GprsMs *ms);
+int ms_new_dl_tbf_assigned_on_pacch(struct GprsMs *ms, struct gprs_rlcmac_tbf *tbf);
+int ms_new_dl_tbf_assigned_on_pch(struct GprsMs *ms);
 int ms_append_llc_dl_data(struct GprsMs *ms, uint16_t pdu_delay_csec, const uint8_t *data, uint16_t len);
 
 static inline bool ms_is_idle(const struct GprsMs *ms)