[#189] sdk/netmap: Refactor Clause enum

Replace alias to v2 type Clause with v2-compatible implementation.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/netmap/clause_test.go

@@ -0,0 +1,31 @@
+package netmap
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/netmap"
+	"github.com/stretchr/testify/require"
+)
+
+func TestClauseFromV2(t *testing.T) {
+	for _, item := range []struct {
+		c   Clause
+		cV2 netmap.Clause
+	}{
+		{
+			c:   0,
+			cV2: netmap.UnspecifiedClause,
+		},
+		{
+			c:   ClauseSame,
+			cV2: netmap.Same,
+		},
+		{
+			c:   ClauseDistinct,
+			cV2: netmap.Distinct,
+		},
+	} {
+		require.Equal(t, item.c, ClauseFromV2(item.cV2))
+		require.Equal(t, item.cV2, item.c.ToV2())
+	}
+}