tests/gb: Show invoked signals in test output

Register an osmo signal handler to print a short notice about every
SS_L_NS signal that is generated while processing the tests.

Sponsored-by: On-Waves ehf
diff --git a/tests/gb/gprs_ns_test.ok b/tests/gb/gprs_ns_test.ok
index 578b905..01b1bc9 100644
--- a/tests/gb/gprs_ns_test.ok
+++ b/tests/gb/gprs_ns_test.ok
@@ -2,6 +2,7 @@
 PROCESSING RESET from 0x01020304:1111
 02 00 81 01 01 82 11 22 04 82 11 22 
 
+==> got signal NS_RESET, NS-VC 0x1122/1.2.3.4:1111
 RESPONSE, msg length 9
 03 01 82 11 22 04 82 11 22 
 
@@ -24,6 +25,7 @@
 PROCESSING UNBLOCK from 0x01020304:1111
 06 
 
+==> got signal NS_UNBLOCK, NS-VC 0x1122/1.2.3.4:1111
 RESPONSE, msg length 1
 07 
 
@@ -42,6 +44,7 @@
 PROCESSING RESET from 0x01020304:2222
 02 00 81 01 01 82 11 22 04 82 11 22 
 
+==> got signal NS_RESET, NS-VC 0x1122/1.2.3.4:2222
 RESPONSE, msg length 9
 03 01 82 11 22 04 82 11 22 
 
@@ -58,6 +61,7 @@
 PROCESSING RESET from 0x01020304:3333
 02 00 81 01 01 82 33 44 04 82 11 22 
 
+==> got signal NS_RESET, NS-VC 0x3344/1.2.3.4:3333
 RESPONSE, msg length 9
 03 01 82 33 44 04 82 11 22 
 
@@ -75,6 +79,7 @@
 PROCESSING RESET from 0x01020304:4444
 02 00 81 01 01 82 11 22 04 82 33 44 
 
+==> got signal NS_RESET, NS-VC 0x1122/1.2.3.4:4444
 RESPONSE, msg length 9
 03 01 82 11 22 04 82 33 44 
 
@@ -92,6 +97,7 @@
 PROCESSING RESET from 0x01020304:3333
 02 00 81 01 01 82 11 22 04 82 11 22 
 
+==> got signal NS_RESET, NS-VC 0x1122/1.2.3.4:3333
 RESPONSE, msg length 9
 03 01 82 11 22 04 82 11 22 
 
@@ -109,6 +115,7 @@
 PROCESSING RESET from 0x01020304:4444
 02 00 81 01 01 82 11 22 04 82 11 22 
 
+==> got signal NS_RESET, NS-VC 0x1122/1.2.3.4:4444
 RESPONSE, msg length 9
 03 01 82 11 22 04 82 11 22