nfp: switch to using data path structures for reconfiguration

Instead of passing around sets of rings and their parameters just
store all information in the data path structure.

We will no longer user xchg() on XDP programs when we swap programs
while the traffic is guaranteed not to be flowing.  This allows us
to simply assign the entire data path structures instead of copying
field by field.

The optimization to reallocate only the rings on the side (RX/TX)
which has been changed is also removed since it seems like it's not
worth the code complexity.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>