#2 Message Integrity Is Not Calculated Correctly

[Duane Murphy]

When the message integrity is added to the stun message, the length field
has not yet been entered. This causes the Message Integrity calculation to
be incorrect.

Add this line before the call to computeHmac() in stunEncodeMessage().

encode16(lengthp, UInt16(ptr - buf - sizeof(StunMsgHdr)
+ sizeof(UInt16) + sizeof(UInt16) + sizeof integrity.hash ));