Pull request 2089: 6420-ipset-header-data-query

Updates #6420.

Squashed commit of the following:

commit 84a2a457bbb923b53880fc4c08e239696b6bda01
Merge: a578fc29d 0e4e243e8
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Nov 30 16:42:48 2023 +0300

    Merge branch 'master' into 6420-ipset-header-data-query

commit a578fc29d7963d819770c7397c2848f815ad4e07
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Nov 30 15:52:42 2023 +0300

    ipset: imp err msg

commit c4673f7e801887b6264bff97271732645fe78d0d
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Wed Nov 29 16:45:36 2023 +0300

    ipset: imp log msg

commit abf8977f55b1be7b51140cfc9bfb402e40efe7c0
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Wed Nov 29 15:29:36 2023 +0300

    ipset: header data query

internal/ipset/ipset_linux_internal_test.go

@@ -47,6 +47,11 @@ func (c *fakeConn) Close() (err error) {
 	return nil
 }
 
+// Header implements the [ipsetConn] interface for *fakeConn.
+func (c *fakeConn) Header(_ string) (_ *ipset.HeaderPolicy, _ error) {
+	return nil, nil
+}
+
 // listAll implements the [ipsetConn] interface for *fakeConn.
 func (c *fakeConn) listAll() (sets []props, err error) {
 	return c.sets, nil