RDMA/bnxt_re: Drop L2 async events silently

In some FW versions, RoCE driver also receives an async notification which
was directed to L2 driver.  RoCE driver does not handle this and print a
message to syslog.  Drop these notifications silently.

Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>