netlink-socket: Exit NL transaction loop when EINVAL is returned

netlink-socket: Exit NL transaction loop when EINVAL is returned

The nl_sock_transact_multiple function enters in an infinite loop,
when invalid error, EINVAL, is returned by nl_sock_transact_multiple__.
EINVAL is the error returned by the latter function when a driver
request fails.

Signed-off-by: Sorin Vinturis <svinturis@cloudbasesolutions.com>
Reported-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Reported-at: https://github.com/openvswitch/ovs-issues/issues/57
Acked-by: Eitan Eliahu <eliahue@vmware.com>
Acked-by: Nithin Raju <nithin@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>