When reading TCP packets with esoteric (or corrupt) values for option types, the asan fsanitize=enum will trigger if the read value is not in range of the enum. The range of a classic (pre-C++11) enum with no negative enumerators is determined by the highest bit set in any of its enumerators, so if `TCP::OptionTypes` has highest enumerator `ALTCHK = 14` it cannot take values above 15.
Define enumerators (per IANA) with bit 7 set to ensure that `TCP::OptionTypes` can take any 8-bit value.
An alternative (C++11 only) would be to give `TCP::OptionTypes` underlying type `uint8_t`.
* Remove option size memers on IP/TCP and instead calculate
these when they're needed
* Reorder members on IP/TCP so as to remove/decrease padding
* Move most memory helpers impl into header file so they
can be inlined
* Make PDUOption's move ctor/assignment operator noexcept
