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_ms_timeout.err b/tests/msc_vlr/msc_vlr_test_ms_timeout.err
index 66ea0bb..653e56c 100644
--- a/tests/msc_vlr/msc_vlr_test_ms_timeout.err
+++ b/tests/msc_vlr/msc_vlr_test_ms_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_ms_timeout_lu_auth_resp
 - Total time passed: 0.000000 s
@@ -129,7 +129,7 @@
 ===== test_ms_timeout_lu_auth_resp: 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_ms_timeout_cm_auth_resp
 - Total time passed: 0.000000 s
@@ -402,7 +402,7 @@
 ===== test_ms_timeout_cm_auth_resp: 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_ms_timeout_paging
 - Total time passed: 0.000000 s
@@ -710,7 +710,7 @@
 ===== test_ms_timeout_paging: 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_classmark_update_timeout
 - Total time passed: 0.000000 s
@@ -863,8 +863,8 @@
 ===== test_classmark_update_timeout: 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