Pull request: 3225 bsd dhcp

Merge in DNS/adguard-home from 3225-bsd-dhcp to master

Closes #3225.
Closes #3417.

Squashed commit of the following:

commit e7ea691824c7ebc8cafd8c9e206679346cbc8592
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 17:02:02 2021 +0300

    all: imp code, docs

commit 5b598fc18a9b69a0256569f4c691bb6a2193dfbd
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 16:28:12 2021 +0300

    all: mv logic, imp code, docs, log changes

commit e3e1577a668fe3e5c61d075c390e4bd7268181ba
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 14:15:10 2021 +0300

    dhcpd: imp checkother

commit 3cc8b058195c30a7ef0b7741ee8463270d9e47ff
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Aug 11 13:20:18 2021 +0300

    all: imp bsd support

internal/aghnet/net_test.go

@@ -1,8 +1,10 @@
 package aghnet
 
 import (
+	"net"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -14,3 +16,51 @@ func TestGetValidNetInterfacesForWeb(t *testing.T) {
 		require.NotEmptyf(t, iface.Addresses, "no addresses found for %s", iface.Name)
 	}
 }
+
+func TestBroadcastFromIPNet(t *testing.T) {
+	known6 := net.IP{
+		1, 2, 3, 4,
+		5, 6, 7, 8,
+		9, 10, 11, 12,
+		13, 14, 15, 16,
+	}
+
+	testCases := []struct {
+		name   string
+		subnet *net.IPNet
+		want   net.IP
+	}{{
+		name: "full",
+		subnet: &net.IPNet{
+			IP:   net.IP{192, 168, 0, 1},
+			Mask: net.IPMask{255, 255, 15, 0},
+		},
+		want: net.IP{192, 168, 240, 255},
+	}, {
+		name: "ipv6_no_mask",
+		subnet: &net.IPNet{
+			IP: known6,
+		},
+		want: known6,
+	}, {
+		name: "ipv4_no_mask",
+		subnet: &net.IPNet{
+			IP: net.IP{192, 168, 1, 2},
+		},
+		want: net.IP{192, 168, 1, 255},
+	}, {
+		name: "unspecified",
+		subnet: &net.IPNet{
+			IP:   net.IP{0, 0, 0, 0},
+			Mask: net.IPMask{0, 0, 0, 0},
+		},
+		want: net.IPv4bcast,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			bc := BroadcastFromIPNet(tc.subnet)
+			assert.True(t, bc.Equal(tc.want), bc)
+		})
+	}
+}