Add a check for consitent U-bit in fragments.
Add a check for consitent U-bit in fragments.

xwhuang/sctp-refimpl,deepak899/sctp-refimpl,sctplab/sctp-refimpl,xwhuang/sctp-refimpl,deepak899/sctp-refimpl,deepak899/sctp-refimpl,deepak899/sctp-refimpl,xwhuang/sctp-refimpl,sctplab/sctp-refimpl,xwhuang/sctp-refimpl,xwhuang/sctp-refimpl,sctplab/sctp-refimpl,deepak899/sctp-refimpl,sctplab/sctp-refimpl,sctplab/sctp-refimpl,deepak899/sctp-refimpl,xwhuang/sctp-refimpl,sctplab/sctp-refimpl