MFC r361313:
Deduplicate fsid comparisons
Comparing fsid_t objects requires internal knowledge of the fsid structure
and yet this is duplicated across a number of places in the code.
Simplify by creating a fsidcmp function (macro).
Reviewed by: mjg, rmacklem
Approved by: mav (mentor)
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D24749