[SCSI] libfcoe: fix VN2VN N_Port_ID Beacon source MAC

FC-BB-6 v1.04 7.9.8.14 N_Port_ID Beacon:

"A N_Port_ID Beacon is multicast and uses the VN_Port MAC address as source
address."

Currently, libfcoe is using ENode MAC, this seems ok and functionality wise
not a problem in my back to back testing setup, however, just fix this to
make libfcoe VN2VN support more spec compliant.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>