vldb_check: fix false mh block error message

Fix a false error message about invalid mh blocks when the vldb has more
than one mh block.  To add insult to injury, vldb_check complains about
the wrong address and block number.

The flags field in the mh block header is in network byte order, in all
of the blocks, not just the first one.  Be sure to convert all of them
to host byte order so the VLCONTBLOCK flag check works.  Fix the error
message on the secondary blocks to show the correct address and block
number.

Example bogus error messages:

vldb_check ./vldb.DB0
address 132120 (offset 0x20458): Multihomed Block 0: Not a multihomed block
address 132120 (offset 0x20458): Multihomed Block 0: Not a multihomed block
address 132120 (offset 0x20458): Multihomed Block 0: Not a multihomed block

Change-Id: I31d96ad43f01fbf2774815184942be45e2d7820b
Reviewed-on: http://gerrit.openafs.org/11555
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: D Brashear <shadow@your-file-system.com>