be2net: do external loopback test only when it is requested

v2: remove unnecessary braces from all 'loopback' if-blocks (thx Sergei)

Cc: sathya.perla@emulex.com
Cc: subbu.seetharaman@emulex.com
Cc: ajit.khaparde@emulex.com
Cc: sergei.shtylyov@cogentembedded.com

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Acked-by: Ajit Khaparde <ajit.khaparde@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>