usrsock: Make the field of usrsock_request native alignment

There is a risk that interfaces such as psock_ioctl/psock_setsockopt
will cause paramete to be not four-byte aligned after calculating the
offset, so align the length of the structure with parameters by four
bytes.

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

drivers/usrsock/usrsock_rpmsg.c

@@ -94,7 +94,6 @@ static int usrsock_rpmsg_send_dns_request(FAR void *arg,
 
   dns->head.reqid = USRSOCK_RPMSG_DNS_REQUEST;
   dns->head.xid = 0;
-  dns->head.reserved = 0;
   dns->addrlen = addrlen;
   memcpy(dns + 1, addr, addrlen);