rocker: fix a sleeping in atomic bug

This code is holding the &ofdpa->flow_tbl_lock spinlock so it is not
allowed to sleep.  That means we have to pass the OFDPA_OP_FLAG_NOWAIT
flag to ofdpa_flow_tbl_del().

Fixes: 936bd486 ("rocker: use FIB notifications instead of switchdev calls")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>