openflow-common: Change flow removal reason codes.

Swap places of OFPRR_METER_DELETE and OFPRR_EVICTION in enumeration to be
compatible with OpenFlow 1.4.

Prior to OpenFlow 1.4 OFPRR_EVICTION was a Nicira specific flow removal reason
code.  OpenFlow 1.3 added support for meters, which require dependent flow
removal when meters are deleted.  The reason code for this is also added in
OpenFlow 1.4, but OFPRR_METER_DELETE now has the value OVS previously had for
OFPRR_EVICTION.

Signed-off-by: Jarno Rajahalme <jarno.rajahalme@nsn.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>