Fix DHCP client to work with qmi_wwan RawIP interface

Makefile

@@ -5,6 +5,7 @@ all: systemd-user-sessions network-config
 	patch -Np1 -d systemd-248 < systemd-248-fix_timesyncd.patch
 	patch -Np1 -d systemd-248 < systemd-248-fix_test-udev.patch
 	patch -Np1 -d systemd-248 < systemd-248-fix_test-path-util.patch
+	patch -Np1 -d systemd-248 < systemd-248-fix_wwan_dhcp.patch
 	patch -Np1 -d systemd-248 < systemd-248-increase_test_timeouts.patch
 	ln -s /tools/bin/true /usr/bin/xsltproc
 	cd systemd-248 && sed -i 's/GROUP="render", //' rules.d/50-udev-default.rules.in

systemd-248-fix_wwan_dhcp.patch

+diff -uNr systemd-248/src/libsystemd-network/sd-dhcp-client.c systemd-248-wwan_dhcp_fix/src/libsystemd-network/sd-dhcp-client.c
+--- systemd-248/src/libsystemd-network/sd-dhcp-client.c	2021-03-31 07:29:02.000000000 +1030
++++ systemd-248-wwan_dhcp_fix/src/libsystemd-network/sd-dhcp-client.c	2026-03-21 23:25:24.603956799 +1030
+@@ -293,16 +293,33 @@
+         bool need_restart = false;
+         int r;
+ 
++        static const uint8_t default_eth_bcast[6] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
++                             default_eth_addr[6]  = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
++
+         assert_return(client, -EINVAL);
+-        assert_return(addr, -EINVAL);
+-        assert_return(addr_len > 0 && addr_len <= MAX_MAC_ADDR_LEN, -EINVAL);
+-        assert_return(arp_type > 0, -EINVAL);
+ 
+         if (arp_type == ARPHRD_ETHER)
+                 assert_return(addr_len == ETH_ALEN, -EINVAL);
+         else if (arp_type == ARPHRD_INFINIBAND)
+                 assert_return(addr_len == INFINIBAND_ALEN, -EINVAL);
+-        else
++        else if (arp_type == ARPHRD_RAWIP || arp_type == ARPHRD_NONE) {
++                /* Linux cellular modem drivers (e.g. qmi_wwan) present a
++                 * network interface of type ARPHRD_RAWIP(519) or
++                 * ARPHRD_NONE(65534) when in point-to-point mode, but these
++                 * are not valid DHCP hardware-type values.
++                 *
++                 * Apparently, it's best to just pretend that these are ethernet
++                 * devices.  Other approaches have been tried, but resulted in
++                 * incompatibilities with some server software.  See
++                 * https://lore.kernel.org/netdev/cover.1228948072.git.inaky@linux.intel.com/
++                 */
++                arp_type = ARPHRD_ETHER;
++                if (addr_len == 0) {
++                        addr = default_eth_addr;
++                        bcast_addr = default_eth_bcast;
++                        addr_len = ETH_ALEN;
++                }
++        } else
+                 return -EINVAL;
+ 
+         if (client->mac_addr_len == addr_len &&
+diff -uNr systemd-248/src/network/networkd-dhcp-common.c systemd-248-wwan_dhcp_fix/src/network/networkd-dhcp-common.c
+--- systemd-248/src/network/networkd-dhcp-common.c	2021-03-31 07:29:02.000000000 +1030
++++ systemd-248-wwan_dhcp_fix/src/network/networkd-dhcp-common.c	2026-03-21 22:26:30.850421741 +1030
+@@ -21,6 +21,12 @@
+         assert(link);
+         assert(IN_SET(family, AF_INET, AF_INET6));
+ 
++        /* Currently, sd-dhcp-client supports only ethernet and infiniband.
++         * (ARMHRD_RAWIP and ARMHRD_NONE are typically wwan modems and will be
++         * treated as ethernet devices.) */
++        if (family == AF_INET && !IN_SET(link->iftype, ARPHRD_ETHER, ARPHRD_INFINIBAND, ARPHRD_RAWIP, ARPHRD_NONE))
++                return false;
++
+         if (family == AF_INET6 && !socket_ipv6_is_supported())
+                 return false;
+