ofproto: Consistently use netdev's name instead of ofp_phy_port name.

There are at least two ways to get an ofport's name: from the netdev using
netdev_get_name() or from the ofp_phy_port's 'name' member.  Some code used
one, some used the other.  This switches all relevant code to use only
netdev_get_name(), because the 'name' member in ofp_phy_port is
fixed-length and thus a long name could be truncated.

This isn't a problem under Linux since the maximum length of a network
device's name under Linux is the same as the field width in ofp_phy_port.