Pull request: all: rm var shadowing, vol. 1

Updates #2803.

Squashed commit of the following:

commit 15fa64ad4fb7561c4b0542245f99869685643bbd
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Mar 11 14:55:28 2021 +0300

    util: imp code

commit c3b0563a44ccc98a5901df19174acdca8a350d62
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Mar 11 14:38:54 2021 +0300

    all: rm var shadowing, vol. 1

internal/util/network.go

@@ -69,7 +69,8 @@ func GetValidNetInterfacesForWeb() ([]*NetInterface, error) {
 	var netInterfaces []*NetInterface
 
 	for _, iface := range ifaces {
-		addrs, err := iface.Addrs()
+		var addrs []net.Addr
+		addrs, err = iface.Addrs()
 		if err != nil {
 			return nil, fmt.Errorf("failed to get addresses for interface %s: %w", iface.Name, err)
 		}