nfp: flower: handle acti_netdevs allocation failure
In the Linux kernel, the following vulnerability has been resolved:

nfp: flower: handle acti_netdevs allocation failure

The kmalloc_array() in nfp_fl_lag_do_work() will return null, if
the physical memory has run out. As a result, if we dereference
the acti_netdevs, the null pointer dereference bugs will happen.

This patch adds a check to judge whether allocation failure occurs.
If it happens, the delayed work will be rescheduled and try again.