net/samba - fix zfs_space related crash

PR: https://github.com/truenas/ports/pull/1167

As of 4.15 tree connect functions in VFS modules must
pass through to vfs_default.c in order for proc_fd support
to be properly initialized in struct connection_struct for
the SMB tree connect. vfs_zfs_space (a legacy VFS module)
did not pass through here and so caused ACL handling code
to hit SMB_ASSERT() that we added to catch any unexpected
internal files_struct that had wrong value set (since this
could have security implications).