Since the deletion of routes with the Nexthop or the Local field set
fails (see the current comment in the code), the Delete function cannot
call the getNetlinkRoute helper.  But since it is not using that helper,
Delete lacks the copy of several important fields in the route to be
deleted, like the source, the priority, the protocol and so on. This can
lead to errors while deleting stale route inserted with the Upsert
function. As an example, let's consider the deletion of the routes added
in the IPSec specific routing table in multi-pool IPAM mode (to be added
soon in a subsequent PR). In that case, with the previous version of the
Delete function, the following error is returned:

`msg="Unable to delete the IPsec route IN from the host routing table" error="no such process"`

and the stale route is not deleted.

The commit fixes the Delete implementation to copy additional fields
from the route.Route internal representation.

Signed-off-by: Fabio Falzoi <[email protected]>