ofproto-dpif-monitor: Remove monitor_init().

Commit 881d47a9fa9 (monitor: Replace monitor_seq with periodic
wakeup.) removes the global "struct seq" in ofproto-dpif-monitor
module.  This change makes the monitor_init() no longer needed.

This commit removes the monitor_init() from ofproto-dpif-monitor.c.

Signed-off-by: Alex Wang <alexw@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
netdev-linux: Drop support for pre-2.6.19 kernels.

The OVS kernel module requires 2.6.32 or later, so there's no reason for
userspace to support older kernels.  This commit removes the special
fallback code for retrieving Linux netdev stats in pre-2.6.19 kernels,
which should no longer be useful.

Signed-off-by: Ben Pfaff <blp@nicira.com>
netdev-linux: Simplify get_stats_via_netlink().

There's no need to obtain the ifindex, because RTM_GETLINK is happy to take
the interface name.  There's no need to do a full nl_policy_parse(),
because we only need a single attribute.

Signed-off-by: Ben Pfaff <blp@nicira.com>