Report physical block size for file-backed LUNs, using vattr.va_blocksize.

MFC after:	1 week

(cherry picked from commit 09b7b8741c34c3bda223d66941ada094af77d794)
(cherry picked from commit 6b93314adf43e0f2d5fc6ef586da6471ee7f5a34)
Remove stale comments.

(cherry picked from commit 5607da901dcfd962c7dc0fdfd4202ce8dd771131)
(cherry picked from commit 6be0e8d9669fce390a16d1a1a7a3b42fd56cc011)
Make VPD 80h (Serial Number) transfer length match serial number length.

MFC after:	1 week

(cherry picked from commit 18b36a84027f81186796361079b04c0d28c14b37)

Ticket:	#6369
(cherry picked from commit f15f1184c0a39304eaf8bce6f1d6eaf4342cb0da)