Handle the "no local address" case in send_sptps_data().

If choose_local_address() is unable to find a local address (e.g.
because of old nodes that don't send their local address information),
then send_sptps_data() ends up using uninitialized variables for the
socket and address.

This regression was introduced in
415910897122da0073a862784d148802ca390020. The commit took care of
handling that case in send_udppacket() but was missing the same fix
for send_sptps_data().

This bug was found by the clang static analyzer tool:
http://clang-analyzer.llvm.org/
Don't initialize outpkt to an unused value.

in receive_udppacket(), we initialize outpkt to a default value but the
value is never read anywhere, as every read is preceded by a write.

This issue was found by the clang static analyzer tool:
http://clang-analyzer.llvm.org/
Remove redundant connection_t::status.active field.

The only places where connection_t::status.active is modified is in
ack_h() and terminate_connection(). In both cases, connection_t::edge
is added and removed at the same time, and that's the only places
connection_t::edge is set. Therefore, the following is true at all
times:

    !c->status.active == !c->edge

This commit removes the redundant state information by getting rid of
connection_t::status.active, and using connection_t::edge instead.
Reserve legacy active bit in connection_status_t.

This is so the positions of the other bits don't change, making it easier to
debug problems with different versions of tinc.

Also fix the padding so connection_status_t is exactly 32 bits.