cfm: Reduce "long delay" message from WARN to INFO, to match BFD behavior.

These messages can cause the testsuite to fail on a busy build machine
since the testsuite treats WARN or ERR log messages as failures.  BFD
uses an INFO message instead of WARN, so this just changes CFM to match.

Alternatively, the testsuite could ignore "long delay" messages (it ignores
some other categories of messages).  In that case I'd expect that we'd
want to change BFD to match CFM since I don't know of a reason why they
should log differently.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Justin Pettit <jpettit@nicira.com>