linuxulator: Return EINVAL for invalid inotify flags

We implement all of the currently-defined Linux inotify mask bits and
flags, with the same values as Linux. Return EINVAL for unknown bits,
as Linux does.

This also moves the translation inline into linux_inotify_add_watch.

Reviewed by: markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D57387

(cherry picked from commit f77d37cffdf3951b7f28b97005467241aa27c183)