RootCanal: Check if Authentication is in progress before starting one

Restarting authentication can override the initiator flag
This was happening when an initiator answered a
LinkKeyRequestNegativeReply

Test: gd/cert/run
Change-Id: Id6e937a29ff64697320fc9b4556069eae2dfd725
Signed-off-by: David Duarte <licorne@google.com>