[rfc] sendfile: refactor out common sendfile code into _do_sendfile()

[Adrian Chadd]

Hi,

http://people.freebsd.org/~adrian/netflix/20140107-freebsd-sendfile-refactor-1.diff

This refactors out the common code from both the sendfile and compat32
sendfile calls into a shared function. That way I can extend the
sendfile behaviour and only have to update one location.

What do people think?



-a