socket-util: extend the buffer in sockaddr_union to make it consistent with hw_addr_data

Concerned by Claude:
https://github.com/systemd/systemd/pull/42119#discussion_r3251133516

src/basic/socket-util.c

@@ -3,6 +3,8 @@
 #include <fcntl.h>
 #include <linux/if.h>
 #include <linux/if_arp.h>
+#include <linux/if_ether.h>
+#include <linux/if_infiniband.h>
 #include <linux/pkt_sched.h>
 #include <mqueue.h>
 #include <net/if.h>