libfcoe: Fix fcoe_sysfs VN2VN mode

The libfc discovery layer is being initialized in the
'create' paths for both legacy libfcoe module parameters
and fcoe_sysfs control interfaces. The problem is that
for VN2VN mode the discovery layer is initialized as if
it were in 'fabric' mode and it is not re-configured when
the mode is changed to 'vn2vn'.

This patch splits out code that needs to be initialized
once and code that can, and should be, re-configured when
the mode changes. Additionally this patch makes that change
so that the discovery layer can be reconfigured to the
libfcoe implementation when in 'vn2vn' mode.

Signed-off-by: Robert Love <robert.w.love@intel.com>
Tested-by: Jack Morgan <jack.morgan@intel.com>
Reviewed-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>