sriov: add support for devlink device parameters and PCIe Sub-Functions (SFs)

[zarkdav]

Description

This PR introduces declarative Netplan support for:

1. Generic & vendor-specific devlink device parameters via devlink-params: (e.g., flow_steering_mode: smfs, lag_port_select_mode: multi-port-esw, enable_roce: true).
2. PCIe Sub-Functions (SFs) via sub-functions: (specifying sfnum, hw-address, and operational state active/inactive).

Example YAML configuration:

network:
  version: 2
  ethernets:
    enp3s0f0np0:
      embedded-switch-mode: switchdev
      devlink-params:
        flow_steering_mode: smfs
      sub-functions:
        - sfnum: 1
          hw-address: 00:11:22:33:44:55
          state: active
        - sfnum: 2
          hw-address: 00:11:22:33:44:56
          state: inactive

Changes Made:

• C ABI & Libnetplan Core:
  • Added devlink_params (GHashTable*) and sub_functions (GArray*) fields to NetplanNetDefinition.
  • Added NetplanSubFunction struct and NetplanSubFunctionState enum in src/abi.h.
  • Added public iterator APIs (_netplan_netdef_new_devlink_params_iter, _netplan_netdef_new_sub_function_iter) in src/util.c.
  • Implemented YAML parsing and validation in src/parse.c.
  • Implemented YAML serialization in src/netplan.c.
  • Updated SR-IOV generator in src/gen-sriov.c to generate netplan-sriov-apply.service when devlink params or sub-functions are present.
• Python CFFI & CLI:
  • Bound new iterators and structs in python-cffi/netplan/_build_cffi.py and python-cffi/netplan/netdef.py.
  • Implemented devlink parameter application and SF lifecycle management (devlink dev param set, devlink port add/function set/activate) in netplan_cli/cli/sriov.py.
• Tests & Documentation:
  • Added C unit tests in tests/ctests/test_netplan_parser.c.
  • Added Python unit tests in tests/test_sriov.py.
  • Documented new properties in doc/netplan-yaml.md.