nfp: prefix vNIC phys_port_name with 'n'

Some drivers are using a bare number inside phys_port_name
as VF id and OpenStack's regexps will pick it up.  We can't
use a bare number for your vNICs, prefix the names with 'n'.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>