Expand LAN to 10.0.0.0/22 with static/reserved/dynamic/spare zones

Splits the LAN into four /24 zones: 10.0.0.0/24 static (no DHCP, DNS
only), 10.0.1.0/24 fixed DHCP reservations by MAC, 10.0.2.0/24 dynamic
DHCP pool, 10.0.3.0/24 spare/unused. ipadm now derives the required
subnet from whether a host has a MAC, auto-assigns free IPs, and
auto-migrates a host's IP when its MAC is added/removed. Migrated the
existing archerc80 reservation from 10.0.0.2 to 10.0.1.2.

Also fixes a latent bug found while doing this: dnsmasq's SIGHUP
(`systemctl reload`) only re-reads /etc/hosts, not the conf-dir files
ipadm writes to, so config changes were silently not applied on
reload. ipadm now restarts dnsmasq instead.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tools/ipadm/host.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"net"
 	"sort"
 	"strings"
 )
@@ -82,3 +83,27 @@ func findByMAC(hosts []Host, mac string, exceptIdx int) int {
 	}
 	return -1
 }
+
+// classifyHostArgs sorts the optional trailing arguments of `ipadm -a` (ip
+// address and/or mac address, in any order, either of which may be omitted)
+// into their fields. Returns an error on unrecognized or duplicate tokens.
+func classifyHostArgs(args []string) (ip, mac string, err error) {
+	for _, a := range args {
+		if _, macErr := net.ParseMAC(a); macErr == nil {
+			if mac != "" {
+				return "", "", fmt.Errorf("MAC address given more than once: %q", a)
+			}
+			mac = a
+			continue
+		}
+		if parsed := net.ParseIP(a); parsed != nil && parsed.To4() != nil {
+			if ip != "" {
+				return "", "", fmt.Errorf("IP address given more than once: %q", a)
+			}
+			ip = a
+			continue
+		}
+		return "", "", fmt.Errorf("unrecognized argument %q (expected IP address or MAC address)", a)
+	}
+	return ip, mac, nil
+}