* nxos_vpc: pkl_vrf fixes for #57069Fixes#57069
- Symptom: When playbooks specify `pkl_vrf: default`, the result is that the cli does not set the `vrf` state.
- Analysis:
- First issue: 'default' is a reserved word when used with the `peer-keepalive` `vrf` keyword. It refers to the default rib.
- This is confusing in several ways because `peer-keepalive`'s *default* vrf is the `management` vrf.
- Second issue: When changing only one optional value (`pkl_vrf`) while other optional values are idempotent (`pkl_src`), the result is that the idempotent values are ignored; unfortunately the device cli *replaces* the entire command, in which case the idempotent values are removed.
- e.g. playbook specifies this:
```
{ pkl_dest: 10.1.1.1, pkl_src: 10.2.2.2, pkl_vrf: my_vrf }
```
```
peer-keepalive dest 10.1.1.1 src 10.2.2.2 # original
peer-keepalive dest 10.1.1.1 src 10.2.2.2 vrf my_vrf # intended result
peer-keepalive dest 10.1.1.1 vrf my_vrf # actual result
```
- Third issue: the `pkl` getter was relying on positional data. This broke when the `udp` keyword nvgen'd where `vrf` used to appear (shifting all keywords to the right).
- Tested on regression platforms: `N3K,N6k,N7K,N9K,N3K-F,N9K-F`
* PEP fixes
* PEP fix 2
* pkl should merge by default, not override
* rmv debugs
* add mike's tests
* fix comments
