arp.h: make struct arpreq four-byte aligned

current sizeof(struct sockaddr_in) is 66

arp/arp_table.c:241:28: runtime error: member access within misaligned address 0xe5f134e6 for type 'struct sockaddr_in', which requires 4 byte alignment
0xe5f134e6: note: pointer points here
 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00
             ^
    #0 0x543287c1 in arp_get_arpreq arp/arp_table.c:241
    #1 0x5432a11f in arp_snapshot arp/arp_table.c:574
    #2 0x5435f0be in netlink_fill_arptable netlink/netlink_route.c:547
    apache#3 0x5435ffca in netlink_get_neighbor netlink/netlink_route.c:715
    apache#4 0x54360116 in netlink_get_neighborlist netlink/netlink_route.c:743
    apache#5 0x54363b20 in netlink_route_sendto netlink/netlink_route.c:1382
    apache#6 0x542ef1b1 in netlink_sendmsg netlink/netlink_sockif.c:625
    apache#7 0x542be94d in psock_sendmsg socket/sendmsg.c:96
    apache#8 0x542bc94b in psock_sendto socket/sendto.c:134
    apache#9 0x542bcb28 in sendto socket/sendto.c:247
    apache#10 0x542bc5ea in send socket/send.c:163
    apache#11 0x542aa715 in netlib_get_arptable /home/mi/gaofengzhi/code/dev1025/apps/netutils/netlib/netlib_getarptab.c:152
    apache#12 0x54279109 in cmd_arp /home/mi/gaofengzhi/code/dev1025/apps/nshlib/nsh_netcmds.c:1197
    apache#13 0x54257faf in nsh_command /home/mi/gaofengzhi/code/dev1025/apps/nshlib/nsh_command.c:1263
    apache#14 0x54231982 in nsh_execute /home/mi/gaofengzhi/code/dev1025/apps/nshlib/nsh_parse.c:718
    apache#15 0x5423da42 in nsh_parse_command /home/mi/gaofengzhi/code/dev1025/apps/nshlib/nsh_parse.c:2619
    apache#16 0x5423e12a in nsh_parse /home/mi/gaofengzhi/code/dev1025/apps/nshlib/nsh_parse.c:2706
    apache#17 0x5424088f in nsh_session /home/mi/gaofengzhi/code/dev1025/apps/nshlib/nsh_session.c:245
    apache#18 0x5422efc9 in nsh_consolemain /home/mi/gaofengzhi/code/dev1025/apps/nshlib/nsh_consolemain.c:75
    apache#19 0x5419e89f in nsh_main /home/mi/gaofengzhi/code/dev1025/apps/system/nsh/nsh_main.c:74
    apache#20 0x54067ee1 in nxtask_startup sched/task_startup.c:70
    apache#21 0x53f366c6 in nxtask_start task/task_start.c:116
    apache#22 0x5409e1a4 in pre_start sim/sim_initialstate.c:52

Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>

Author: zhhyu7

include/netinet/arp.h

@@ -65,7 +65,7 @@
 
 /* All ARP ioctls take a pointer to a struct arpreq as their parameter: */
 
-struct arpreq
+struct aligned_data(sizeof(FAR void *)) arpreq
 {
   struct sockaddr arp_pa;                /* Protocol address */
   struct sockaddr arp_ha;                /* Hardware address */