fusefs: Upgrade FUSE protocol to version 7.35.

Upgrade the FUSE API from protocol 7.33 to 7.35.
Add support for FOPEN_NOFLUSH, introduced in 7.35.

Also, reduce diffs vis-a-vis upstream by factoring out an ioctl type, a
change missed in d5e3cf41e89.

Signed-off-by: Claudiu I. Palincas <mscotty@protonmail.ch>
Reviewed by: asomers
Pull Request: https://github.com/freebsd/freebsd-src/pull/1744