Add/use defines for max buffer size and path len
Add/use defines for max buffer size and path len

Use PATH_MAX for max configfs path len.

Add define for max configfs buffer size.

Signed-off-by: Mike Christie <39daeb1549a929782e38aa87c4e3da7f3844b09a@redhat.com>

open-iscsi/tcmu-runner,agrover/tcmu-runner,liuy/tcmu-runner,open-iscsi/tcmu-runner