Before, when tinc saw a packet larger than the PMTU with a VLAN tag, it would
not know what to do with it, and would just forward it via TCP. Now, tinc
handles 802.1q packets correctly, as long as there is only one tag.
The utility functions in the lib/ directory do not really form a library.
Also, now that we build two binaries, tincctl does not need everything that was
in libvpn.a, so it is wasteful to link to it.
