tbf: Drop unneeded method set_tlli_from_ul

Since commit 322456ed474a733094c9f3e240295b469023ad14 (and previous
one), it is expected that a tbf object ALWAYS has a MS object referend
to it, even if it's a temporary copy which will later be merged when
TLLI/IMSI is retrieved and it is found that several MS objects relate to
the same MS.

The purpose of set_tlli_from_ul was mainly to update TBF's ms() to
old_ms before going through usual tbf->update_ms() path. That's not
really needed since ms() is already always set and TBFs for old_ms are
already freed in update_ms() and children function.

Change-Id: Ie8795e7a02032336e53febb65c11f9150c36d2a0
diff --git a/tests/tbf/TbfTest.err b/tests/tbf/TbfTest.err
index 827f5ce..0d097ee 100644
--- a/tests/tbf/TbfTest.err
+++ b/tests/tbf/TbfTest.err
@@ -2079,7 +2079,6 @@
 TBF(TFI=0 TLLI=0x00000000 DIR=UL STATE=FLOW) BSN 0 storing in window (0..63)
 TBF(TFI=0 TLLI=0x00000000 DIR=UL STATE=FLOW) data_length=20, data=f1 22 33 44 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
 TBF(TFI=0 TLLI=0x00000000 DIR=UL STATE=FLOW) Decoded premier TLLI=0xf1223344 of UL DATA TFI=0.
-TBF(TFI=0 TLLI=0xf1223344 DIR=DL STATE=ASSIGN) Got RACH from TLLI=0xf1223344 while TBF still exists: killing pending DL TBF
 TBF(TFI=0 TLLI=0xf1223344 DIR=DL STATE=ASSIGN) changes state from ASSIGN to RELEASING
 TBF(TFI=0 TLLI=0xf1223344 DIR=DL STATE=RELEASING) free
 TBF(TFI=0 TLLI=0xf1223344 DIR=DL STATE=RELEASING) stopping timer T0 [freeing TBF]
@@ -2089,8 +2088,8 @@
 Modifying MS object, TLLI = 0x00000000, IMSI '' -> '0011223344'
 Modifying MS object, TLLI = 0x00000000, MS class 0 -> 1
 Clearing MS object, TLLI: 0xf1223344, IMSI: '0011223344'
-Modifying MS object, UL TLLI: 0x00000000 -> 0xf1223344, not yet confirmed
 Destroying MS object, TLLI = 0x00000000
+Modifying MS object, UL TLLI: 0x00000000 -> 0xf1223344, not yet confirmed
 TBF(TFI=0 TLLI=0xf1223344 DIR=UL STATE=FLOW) Assembling frames: (len=20)
 TBF(TFI=0 TLLI=0xf1223344 DIR=UL STATE=FLOW) Frame 1 starts at offset 4, length=16, is_complete=1
 TBF(TFI=0 TLLI=0xf1223344 DIR=UL STATE=FLOW) complete UL frame len=16