SGSN: split GEA key management from TLLI

Move GEA key from TLLI assignment into separate function.

Change-Id: I8a0bc907072dc19cd9535a28b5252dc0f05357cc
Related: OS#1582
diff --git a/openbsc/src/gprs/gprs_sgsn.c b/openbsc/src/gprs/gprs_sgsn.c
index 98439de..711887e 100644
--- a/openbsc/src/gprs/gprs_sgsn.c
+++ b/openbsc/src/gprs/gprs_sgsn.c
@@ -244,7 +244,7 @@
 
 	if (llme) {
 		/* TLLI unassignment, must be called after sgsn_mm_ctx_free */
-		gprs_llgmm_assign(llme, tlli, 0xffffffff, GPRS_ALGO_GEA0, NULL);
+		gprs_llgmm_assign(llme, tlli, 0xffffffff);
 	}
 }