bnxt_en: Add unsupported SFP+ module warnings.

Add the PORT_CONN_NOT_ALLOWED async event handling logic.  The driver
will print an appropriate warning to reflect the SFP+ module enforcement
policy done in the firmware.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>