[#xx] Add support for SELECT-FILTER expressions

Signed-off-by: Alejandro Lopez <a.lopez@yadro.com>

netmap/parser/query_visitor.go

@@ -11,6 +11,9 @@ type QueryVisitor interface {
 	// Visit a parse tree produced by Query#policy.
 	VisitPolicy(ctx *PolicyContext) interface{}
 
+	// Visit a parse tree produced by Query#selectFilterExpr.
+	VisitSelectFilterExpr(ctx *SelectFilterExprContext) interface{}
+
 	// Visit a parse tree produced by Query#repStmt.
 	VisitRepStmt(ctx *RepStmtContext) interface{}