cfm: Remove sequence fault reason.

cfm: Remove sequence fault reason.

Commit 2b540ecb (Added handling of previously ignored cfm faults.)
made the CFM code trigger a fault when a packet is received with an
out of order sequence number.  This means that if even one CFM
probe is dropped, a fault will be triggered because the next
received probe's sequence would be two greater than the last.  This
is in conflict with the 802.1ag requirement that 3.5 dropped probes
triggers fault.

Signed-off-by: Ethan Jackson <ethan@nicira.com>