tweak tun/tap kn_data to be more consistent with everything else.

for EVFILT_READ, kn_data is now like FIONREAD and reports how many
bytes there are to read. previously it would report how many packets
were available to read, which is not something i've seen anywhere
else.

for EVFILT_WRITE, report the max number of bytes a write can do.
previously it was if_mtu bytes, now it is if_hdrlen + if_hardmtu
bytes, which is the same as what the write path uses as it's maximum
message size.

discussed with and ok visa@

0 files changed, 0 insertions, 0 deletions