BIGIP-13 version enrollment requires mgmt IFACE support vs ETH0

[ssorenso]

• TITLE: BIGIP-13 version enrollment requires mgmt IFACE support vs ETH0
• Summary:
  • MGMT is used instead of ETH0 in BIGIP-13 for management purposes
  • Currently, the handling method for this set_iface_value has a syntax error and is not dynamic
  • Needs to have the ability to dynamically handle upcoming versions, not just 13

[dflanigan]

@ssorenso we need a pr from your fork.