non-blocking BPF reads return -1/EWOULDBLOCK until the store buffer fills up

[Matthew Dillon]

:To reproduce, compile the attached (C++) program, run it on an adapter =
:with the filter "icmp" on a reasonably quiet network, and then, on the =
:same machine, ping some host the pings to which will go out on the same =
:network. Note that the program doesn't report any packets having been =
:seen.
:
:To fix, apply the attached patch.  (A similar bug has been filed against =
:FreeBSD - and will be filed against Mac OS X.)

    Thanks for the bug report Guy!  I've committed the patch.

						-Matt