NS: Factor out gprs_nsvc_start_test() and use it

This function performs  sending a NS-ALIVE PDU and starting Tns-Test,
let's use it in all places where we used to do that.

As part of this, also fix a bug where the sendto() return value (number
of bytes sent) would actually propagate up all the way to
gprs_ns_rx_reset() return value, which in turn affects the test results
on stdout.

Change-Id: I4d303117f77fabb74bbb91887b9914a81c2a084a
diff --git a/tests/gb/gprs_ns_test.ok b/tests/gb/gprs_ns_test.ok
index 3cb1dfc..57ae188 100644
--- a/tests/gb/gprs_ns_test.ok
+++ b/tests/gb/gprs_ns_test.ok
@@ -344,7 +344,7 @@
 MESSAGE to BSS, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 Current NS-VCIs:
     VCI 0x2001, NSEI 0x2000, peer 0x01020304:2222, ALIVE, UNBLOCKED, UNRESET
@@ -365,7 +365,7 @@
 MESSAGE to BSS, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 Current NS-VCIs:
     VCI 0x2001, NSEI 0x2000, peer 0x00000000:0, DEAD, BLOCKED, RESET
@@ -386,7 +386,7 @@
 MESSAGE to BSS, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 Current NS-VCIs:
     VCI 0x2001, NSEI 0x2000, peer 0x00000000:0, DEAD, BLOCKED, RESET
@@ -534,7 +534,7 @@
 MESSAGE to BSS, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 Current NS-VCIs:
     VCI 0xf001, NSEI 0x1000, peer 0x00000000:0, ALIVE, BLOCKED, UNRESET
@@ -557,7 +557,7 @@
 MESSAGE to BSS, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 Current NS-VCIs:
     VCI 0xf001, NSEI 0x1000, peer 0x01020304:2222, ALIVE, BLOCKED, UNRESET
@@ -641,7 +641,7 @@
 MESSAGE to BSS, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 Current NS-VCIs:
     VCI 0xf001, NSEI 0x1000, peer 0x00000000:0, ALIVE, BLOCKED, UNRESET
@@ -666,7 +666,7 @@
 MESSAGE to SGSN, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 PROCESSING ALIVE_ACK from 0x05060708:32000
 0b 
@@ -818,7 +818,7 @@
 MESSAGE to SGSN, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 PROCESSING ALIVE_ACK from 0x05060708:32000
 0b 
@@ -898,7 +898,7 @@
 MESSAGE to SGSN, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 PROCESSING ALIVE_ACK from 0x05060708:32000
 0b 
@@ -956,7 +956,7 @@
 MESSAGE to SGSN, msg length 1
 0a 
 
-result (RESET_ACK) = 1
+result (RESET_ACK) = 0
 
 PROCESSING ALIVE_ACK from 0x05060708:32000
 0b