net: tftp: Fix tftp_prev_block counter update

Fixes missing update to tftp_prev_block counter before increase
tftp_cur_block counter when do the tftpput operation.

tftp_prev_block counter is used in update_block_number() function to
check whether block number (sequence number) is rollover. This bug
cause the tftpput command fail to upload a large file when block
number is greater than 16-bit (0xFFFF).
Signed-off-by: NLey Foon Tan <ley.foon.tan@intel.com>
Reviewed-By: NRamon Fried <rfried.dev@gmail.com>

net/tftp.c

@@ -502,6 +502,7 @@ static void tftp_handler(uchar *pkt, unsigned dest, struct in_addr sip,
 				int block = ntohs(*s);
 				int ack_ok = (tftp_cur_block == block);
 
+				tftp_prev_block = tftp_cur_block;
 				tftp_cur_block = (unsigned short)(block + 1);
 				update_block_number();
 				if (ack_ok)