ovs-hyperv: make kernel return values netlink socket like

ovs-hyperv: make kernel return values netlink socket like

In this patch, we make changes to usersapce as well as
kernel datapath on hyperv to make it more netlink socket
like. Previously, the kernel datapath did not distinguish
between "transport errors" and other errors. Netlink
semantics dictate that netlink functions should only
return an error only in the case of a "transport error"
which is generally something fatal. Eg. failure to
communicate with the OVS module, or an invalid command
altogether. Other errors such as an unsupported action,
or an invalid flow key is not considered a "transport
error", and in such cases, netlink functions are to return
success with a 'struct nlmsgerr' populated in the output
buffer.

This patch implements these semantics.

Signed-off-by: Nithin Raju <nithin@vmware.com>
Acked-by: Sorin Vinturis <svinturis@cloudbasesolutions.com>
Reported-at: https://github.com/openvswitch/ovs-issues/issues/72
Signed-off-by: Ben Pfaff <blp@nicira.com>