fs: Add freezing handling to mnt_want_write() / mnt_drop_write()

fs: Add freezing handling to mnt_want_write() / mnt_drop_write()

Most of places where we want freeze protection coincides with the places where
we also have remount-ro protection. So make mnt_want_write() and
mnt_drop_write() (and their _file alternative) prevent freezing as well.
For the few cases that are really interested only in remount-ro protection
provide new function variants.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <[email protected]>
Tested-by: Peter M. Petrakis <[email protected]>
Tested-by: Dann Frazier <[email protected]>
Tested-by: Massimo Morana <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Signed-off-by: Al Viro <[email protected]>