[#354] api/netmap: Return a slice of parameters directly

`IterateParameters` does a poor job:
- it doesn't encapsulate well, because it returns a pointer,
- it has a clunky interface, compared to range loop.

I have decided to return parameter slice and not `iter.Seq` for 2
reasons:
1. There already is `SetParameters`, so `NetworkConfig` struct is
   expected to be modified.
2. This iterator uses pointers, so even with this interface the slice
   can already be changed.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

netmap/network_info_test.go

@@ -76,16 +76,10 @@ func testConfigValue(t *testing.T,
 		var m netmap.NetworkInfo
 		x.WriteToV2(&m)
 
-		require.EqualValues(t, 1, m.GetNetworkConfig().NumberOfParameters())
-		found := false
-		m.GetNetworkConfig().IterateParameters(func(prm *netmap.NetworkParameter) bool {
-			require.False(t, found)
-			require.Equal(t, []byte(v2Key), prm.GetKey())
-			require.Equal(t, v2Val(exp), prm.GetValue())
-			found = true
-			return false
-		})
-		require.True(t, found)
+		var p netmap.NetworkParameter
+		p.SetKey([]byte(v2Key))
+		p.SetValue(v2Val(exp))
+		require.Equal(t, []netmap.NetworkParameter{p}, m.GetNetworkConfig().Parameters())
 	}
 
 	setter(&x, val1)