Fix inode birthtime updating.

[fsu]

Summary

The birthtime field of struct vattr does not checked for VNOVAL in case of ext2_setattr() and produce incorrect inode birthtime values.

Test Plan

Found using pjdfstest: pjdfstest/tests/utimensat/03.t.
Testcase passed after fix.

[pfg]

Minor knits, otherwise LGTM.

sys/fs/ext2fs/ext2_vnops.c

380

Not needed because the macro has parenthesis already (standard practice).

509–512

Invert the order: whe should verify if E2DI_AS_XTIME first and only then check for VNOVAL.

[fsu]

Fix and expression order.

[fsu]

sys/fs/ext2fs/ext2_vnops.c

380

May be let's leave it as is. The concern is, that if expression without braces looks strange. Also, we have same if expressions with braces in the ext2_inode_cnv.c.