usnic: add missing clauses to BSD license

The usnic_verbs kernel module was clearly marked with the following in
its code:

  MODULE_LICENSE("Dual BSD/GPL");

However, we accidentally left a few clauses of the BSD text out of the
license header in all the source files.  This commit fixes that: all
the files are properly dual BSD/GPL-licensed.  Contributors that might
have been confused by this have been contacted to get their permission
and are Cc:ed here.

Cc: Benoit Taine <benoit.taine@lip6.fr>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Masanari Iida <standby24x7@gmail.com>
Cc: Matan Barak <matanb@mellanox.com>
Cc: Michael Wang <yun.wang@profitbricks.com>
Cc: Roland Dreier <roland@purestorage.com>
Cc: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>