net/can: Add SO_RCVBUF option for can socket

[HedongGao]

Summary

If the CAN stack receiving packets fast, but the application layer reading packets slow. Then conn->readahead will continue to grow, leading to memory leaks. Finally CAN stack potentially starve out all IOB buffers.

To prevent IOB buffers leaks, users can restrict CAN socket buffer length.

Impact

Rename mm/iob/iob_get_queue_size.c to mm/iob/iob_get_queue_info.c
Discard subsequent CAN frame， when the CAN socket is full.

Testing

CAN socket can cache x packets. x = (NET_MAX_RECV_BUFSIZE + IOB_BUF_SIZE - 1)/IOB_BUF_SIZE
Set NET_MAX_RECV_BUFSIZE = 1024 when make-menuconfig.
CAN Socket could cache 6 packets.

Create a demo program as follows:
`
int main(int argc, char **argv)
{
int fd;
int buf_size;
struct ifreq ifr_can;
struct sockaddr_can can_addr_can;

fd = socket(PF_CAN, SOCK_RAW, CAN_RAW);
strcpy(ifr_can.ifr_name, "can0");
ioctl(fd, SIOCGIFINDEX, &ifr_can);
can_addr_can[i].can_family = AF_CAN;
can_addr_can.can_ifindex = ifr_can.ifr_ifindex;
bind(fd, (struct sockaddr*)&can_addr_can, sizeof(can_addr_can));
//setsockopt(fd, SOL_CAN_RAW, SO_RCVBUF, &buf_size, sizeof(buf_size));

while(1){
    sleep(3);
    //Do not read CAN frame or reading speed slower than writing speed.
}
return 0;

}
`
CAN stack potentially starve out all IOB buffers if do not set SO_RCVBUF option.

[acassis]

@HedongGao please add that text from Summary into your commit log

[HedongGao]

Add Summary-text into commit log！