datapath: Use openvswitch_handle_frame hook in >=RHEL6.4 to live side by side with bridging

Due to the missing register rx_handler API in the kernel RHEL6 is
based on, the datapath currently falls back to using the bridging
hook with the consequence that bridging and OVS cannot be used in
parallel on any RHEL6 release.

For this purpose, >=RHEL6.4 releases provide a special rx frame hook
to be used by OVS. It captures frames at the same location in the
stack as the rx_handler would do in more recent kernel releases. In
order to store the vport pointer, the net_device's ax25_ptr field is
utilized under the assumption that an AX25 device will never be
attached to an OVS bridge.

Signed-off-by: Thomas Graf <tgraf@redhat.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
datapath: Account for RHEL6.4 backports in compat layer

Explicitly check the availability of several kernel API functions
instead of relying on the kernel version to account for Red Hat
Enterprise Linux backports.

Signed-off-by: Thomas Graf <tgraf@redhat.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
bridge: Report PID of yielding process when multiple instances run.

Normally, the daemon code will detect when multiple instances are run
and print the conflicting PID.  However, if ovs-vswitchd is not run in
daemon mode or the pidfile is removed, a database lock is checked.  The
message it prints wasn't specific enough about which process was backing
off due to not getting the lock.

Signed-off-by: Justin Pettit <jpettit@nicira.com>