update bnx firmware to the latest version in FreeBSD:

6.0.15 for BCM5706 and BCM5708
6.0.17 for BCM5709 and BCM5716

Tested on BCM5708 by naddy, BCM5716 by sthen and BCM5709 by myself.

ok deraadt@

correctly list which files this license applies to

build a bnx firmware file, for firmload