net/mlx5e: Support multiple encapsulations for a TC flow

Currently a flow is associated with a single encap structure. The FW
extended destination features enables the driver to associate a flow
with multiple encap instances.

Change the encap id field from a flow scope to a per destination value
in the flow attributes struct. Use the encaps array to associate a flow
table entry with multiple encap entries.

Update the neigh logic to offload only if all encapsulations used in a
flow are connected, and un-offload upon the first one disconnected.

Note that the driver can now support up to two encap destinations.

Signed-off-by: Eli Britstein <elibr@mellanox.com>
Reviewed-by: Oz Shlomo <ozsh@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>