octeontx2-pf: Fix ndo_set_rx_mode

Since set_rx_mode takes a mutex lock for sending mailbox
message to admin function to set the mode, moved logic
to a workqueue.

Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>