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_openbsd_test.go

@@ -0,0 +1,52 @@
+//go:build openbsd
+// +build openbsd
+
+package aghnet
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHostnameIfStaticConfig(t *testing.T) {
+	const nl = "\n"
+
+	testCases := []struct {
+		name       string
+		rcconfData string
+		wantHas    bool
+	}{{
+		name:       "simple",
+		rcconfData: `inet 127.0.0.253` + nl,
+		wantHas:    true,
+	}, {
+		name:       "case_sensitiveness",
+		rcconfData: `InEt 127.0.0.253` + nl,
+		wantHas:    false,
+	}, {
+		name: "comments_and_trash",
+		rcconfData: `# comment 1` + nl +
+			`` + nl +
+			`# inet 127.0.0.253` + nl +
+			`inet` + nl,
+		wantHas: false,
+	}, {
+		name: "incorrect_config",
+		rcconfData: `inet6 127.0.0.253` + nl +
+			`inet 256.256.256.256` + nl,
+		wantHas: false,
+	}}
+
+	for _, tc := range testCases {
+		r := strings.NewReader(tc.rcconfData)
+		t.Run(tc.name, func(t *testing.T) {
+			has, err := hostnameIfStaticConfig(r)
+			require.NoError(t, err)
+
+			assert.Equal(t, tc.wantHas, has)
+		})
+	}
+}