bsc: si: Fix SI2ter L2 pseudo length

3GPP TS 04.08 V7.21.0, section "9.1.34 System information type 2ter"
states:

"""
This message has a L2 pseudo length of 18. This message may be sent
by the network with either a L2 pseudo length of 18 or some other
value. A mobile station that does not ignore this message shall not
discard the message due to a received L2 pseudo length different
from 18.
"""

Change-Id: I45cb217ebdf89b82b0f37f38eef7a1e3a651f541
diff --git a/tests/gsm0408/gsm0408_test.ok b/tests/gsm0408/gsm0408_test.ok
index 0c6df7a..b083f08 100644
--- a/tests/gsm0408/gsm0408_test.ok
+++ b/tests/gsm0408/gsm0408_test.ok
@@ -214,7 +214,7 @@
 Testing if BA-IND is set as expected in SI2xxx and SI5xxx
 SI2: 59 06 1a 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 e5 04 00 
 SI2bis: 55 06 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 e5 04 00 2b 
-SI2ter: 59 06 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 2b 2b 2b 2b 
+SI2ter: 49 06 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 2b 2b 2b 2b 
 SI5: 06 1d 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
 SI5bis: 06 05 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
 SI5ter: 06 06 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00