Partially revert "*: use localhost address instead of 127.0.0.1, fix #2575"

This partially reverts commit c26a962b55 for testing
chains configurations.

Ref. #2975, although this commit doesn't close it. This commit is an attempt to
enforce IPv4 for our test clients to avoid problem described in the issue.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

config/protocol.unit_testnet.single.yml

@@ -58,7 +58,7 @@ ApplicationConfiguration:
     MaxGasInvoke: 15
     Enabled: true
     Addresses:
-      - "localhost:0" # let the system choose port dynamically
+      - "127.0.0.1:0" # let the system choose port dynamically
     EnableCORSWorkaround: false
   Prometheus:
     Enabled: false #since it's not useful for unit tests.

config/protocol.unit_testnet.yml

@@ -12,9 +12,9 @@ ProtocolConfiguration:
     - 02c4de32252c50fa171dbe25379e4e2d55cdc12f69e382c39f59a44573ecff2f9d
   ValidatorsCount: 4
   SeedList:
-    - localhost:20334
-    - localhost:20335
-    - localhost:20336
+    - 127.0.0.1:20334
+    - 127.0.0.1:20335
+    - 127.0.0.1:20336
   VerifyTransactions: true
   P2PSigExtensions: true
   NativeActivations:
@@ -62,7 +62,7 @@ ApplicationConfiguration:
     MaxGasInvoke: 15
     Enabled: true
     Addresses:
-      - "localhost:0" # let the system choose port dynamically
+      - "127.0.0.1:0" # let the system choose port dynamically
     EnableCORSWorkaround: false
     SessionEnabled: true
     SessionExpirationTime: 2 # enough for tests as they run locally.

pkg/network/payload/address_test.go

@@ -14,7 +14,7 @@ import (
 
 func TestEncodeDecodeAddress(t *testing.T) {
 	var (
-		e, _ = net.ResolveTCPAddr("tcp", "localhost:2000")
+		e, _ = net.ResolveTCPAddr("tcp", "127.0.0.1:2000")
 		ts   = time.Now()
 		addr = NewAddressAndTime(e, ts, capability.Capabilities{
 			{
@@ -45,7 +45,7 @@ func TestEncodeDecodeAddress(t *testing.T) {
 
 func fillAddressList(al *AddressList) {
 	for i := 0; i < len(al.Addrs); i++ {
-		e, _ := net.ResolveTCPAddr("tcp", fmt.Sprintf("localhost:20%d", i))
+		e, _ := net.ResolveTCPAddr("tcp", fmt.Sprintf("127.0.0.1:20%d", i))
 		al.Addrs[i] = NewAddressAndTime(e, time.Now(), capability.Capabilities{
 			{
 				Type: capability.TCPServer,