Eliminate QETH debugging DEBUG build dependency:

Debug messages controlled by devstmt 'debug' option, not how QETH was built.
Fix QETH raise interrupt locking as per Mark G.
Fix MTU and makepfxmask4 bugs in QETH
QETH temp 'setip' opt == Windows default
QETH ipaddr/netmask fixes (for pre-config tun dev support)
L3/IP packet filtering:

Similar to L2/MAC filtering. Not sure if this is needed for *nix tun devices, but we'll eventually need something like it for VIPA support, and Windows needs it now.
QETH: 1) trash bogus/temporary 'noiq' "no i/p queue" flag/interrupt, 2) fix queues mask race between Activate Queues and Signal Adapter.