Set format value properly while setting packet-in format

The format value is expected in big-endian, so OVS was responding
with OFPBRC_EPERM to set packet-in format requests.

Change-Id: I49b65fa96c5aad8c3b26874a6e364d3dcf64f19e
Signed-off-by: Amit Bose <bose@noironetworks.com>