Is there anyway to modify the MTU size in the io-pkt stack?  If yes, please let me know where and all I need to do the 
same?

I have requirement to add few bytes before the ethernet header, this is done in if_bridge.c file.  So along with this 
addition the packet length should not cross what is configured in the stack for ethernet transmission.  So i prefer to 
block the same in io-pkt such that TCP socket fragmentation will not cross the configured packet limit.

Please guide me in this.