ofproto: Ditch SLOW_IN_BAND slow path reason.

ofproto: Ditch SLOW_IN_BAND slow path reason.

Before this patch, when in band control was enabled, every DHCP
packet had to be sent to userspace to calculate it's actions.
Those DHCP packets intended for the local port would have a special
action added to ensure they actually make it there.  This
unnecessarily complicates the code, so this patch takes a slightly
different approach.  When in-band is enabled, *all* DHCP packets
must be sent to the local port.  This guarantees that
xlate_actions() returns the same result every time for a given
flow.

Signed-off-by: Ethan Jackson <ethan@nicira.com>