Building on Rocky 9.6

First time trying to build nullfsvfs, was getting:

```
$ make
make -C /lib/modules/5.14.0-570.19.1.el9_6.x86_64/build M=/home/devin/nullfsvfs-0.19 modules
make[1]: Entering directory '/usr/src/kernels/5.14.0-570.19.1.el9_6.x86_64'
CC [M] /home/devin/nullfsvfs-0.19/nullfs.o
/home/devin/nullfsvfs-0.19/nullfs.c: In function ‘nullfs_getattr’:
/home/devin/nullfsvfs-0.19/nullfs.c:159:26: error: passing argument 1 of ‘generic_fillattr’ from incompatible pointer type [-Werror=in
compatible-pointer-types]
159 | generic_fillattr(&init_user_ns, inode, stat);
| ^~~~~~~~~~~~~
| |
| struct user_namespace *
```
(and a lot of additional "incompatible pointer" errors). I was able to disable this check by adding

```
EXTRA_CFLAGS += -Wno-incompatible-pointer-types
```

to the Makefile. I'm not sure if this is safe to do, but it _seems_ to be working.