tests: Avoid hash order sensitivity in "ofproto - flow monitoring" test.

The order in which flows appear in an NXST_FLOW_MONITOR reply depends on
the hash order, which makes it depend on the details of the hash and on
system endianness.  This avoids sensitivity to the order by sorting the
results.

Reported-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Pfaff <blp@nicira.com>