libtcmu: fix inquiry buffer length calculations
libtcmu: fix inquiry buffer length calculations

The tcmu device config string is added as an entry in the device
identification page, which has a corresponding one-byte length stored
and later retrieved (for length calculations) from a char ptr.

If device config string length exceeds 127 characters (char maximum)
then subsequent length calculations are done using a wrapped value.

Bug: https://github.com/open-iscsi/tcmu-runner/issues/76

Signed-off-by: David Disseldorp <589a549dc9f982d9f46aeeb82a09ab6d87ccf1d8@suse.de>

open-iscsi/tcmu-runner,lxbsz/tcmu-runner,open-iscsi/tcmu-runner,liuy/tcmu-runner,superlibj/tcmu-runner,agrover/tcmu-runner,JefferyHu/tcmu-runner