From: Brian Behlendorf <behlendorf1@llnl.gov>
Subject: [PATCH] fix stack dsl_scan_visitbp

To reduce stack overhead this topic branch moves the 128 byte
blkptr_t data strucutre in dsl_scan_visitbp() to the heap.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>