Linux 6.6 compat: generic_fillattr has a new u32 request_mask added at arg2

In commit 0d72b92883c651a11059d93335f33d65c6eb653b, a new u32 argument
for the request_mask was added to generic_fillattr. This is the same
request_mask for statx that's present in the most recent API implemented
by zpl_getattr_impl. This commit conditionally adds it to the
zpl_generic_fillattr(...) macro, as well as the zfs_getattr_fast(...)
implementation, when configure determines it's present in the kernel's
generic_fillattr(...).

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #15263