ext4: Add feature set check helper for mount & remount paths
A user reported that although his root ext4 filesystem was mounting
fine, other filesystems would not mount, with the:
"Filesystem with huge files cannot be mounted RDWR without CONFIG_LBDAF"
error on his 32-bit box built without CONFIG_LBDAF. This is because
the test at mount time for this situation was not being re-checked
on remount, and the normal boot process makes an ro->rw transition,
so this was being missed.
Refactor to make a common helper function to test the filesystem
features against the type of mount request (RO vs. RW) so that we
stay consistent.
Addresses Red-Hat-Bugzilla: #517650
Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>