add rudimentary NRI support for MSC pooling

This patch served for a manual testing counterpart for osmo-bsc to implement
MSC pooling.

This enables a basic MSC pooling setup, but for a production setup, osmo-msc
would still lack various features related to unloading subscribers to another
MSC as explained in 3GPP TS 23.236.

Change-Id: Iafe0878a0a2c8669080d757b34a398ea75fced36
diff --git a/tests/msc_vlr/msc_vlr_test_hlr_timeout.err b/tests/msc_vlr/msc_vlr_test_hlr_timeout.err
index 3717533..d68b4f7 100644
--- a/tests/msc_vlr/msc_vlr_test_hlr_timeout.err
+++ b/tests/msc_vlr/msc_vlr_test_hlr_timeout.err
@@ -1,6 +1,6 @@
 DLMGCP MGCP client: using endpoint domain '@mgw'
 full talloc report on 'msgb' (total      0 bytes in   1 blocks)
-talloc_total_blocks(tall_bsc_ctx) == 19
+talloc_total_blocks(tall_bsc_ctx) == 20
 
 ===== test_hlr_timeout_lu_auth_info
 - Total time passed: 0.000000 s
@@ -110,7 +110,7 @@
 ===== test_hlr_timeout_lu_auth_info: SUCCESS
 
 full talloc report on 'msgb' (total      0 bytes in   1 blocks)
-talloc_total_blocks(tall_bsc_ctx) == 19
+talloc_total_blocks(tall_bsc_ctx) == 20
 
 ===== test_hlr_timeout_lu_upd_loc_result
 - Total time passed: 0.000000 s
@@ -237,8 +237,8 @@
 ===== test_hlr_timeout_lu_upd_loc_result: SUCCESS
 
 full talloc report on 'msgb' (total      0 bytes in   1 blocks)
-talloc_total_blocks(tall_bsc_ctx) == 19
+talloc_total_blocks(tall_bsc_ctx) == 20
 
 full talloc report on 'msgb' (total      0 bytes in   1 blocks)
-talloc_total_blocks(tall_bsc_ctx) == 19
+talloc_total_blocks(tall_bsc_ctx) == 20