Teach zdb(8) how to obtain GEOM provider size.
Teach zdb(8) how to obtain GEOM provider size.

PR:		kern/133134
Reported by:	Philipp Wuensche <cryx-freebsd@h3q.com>
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase