GATEWAYS-4422 - Add DumpPortMappings API to retrieve ofport and MAC address for tap interfaces

[yrkurapati]

JIRA Ticket: https://do-internal.atlassian.net/browse/GATEWAYS-4422

• Adds new DumpPortMappings method to retrieve port mappings for all interfaces from Open vSwitch bridges
• Parses ovs-ofctl show output to extract ofport numbers and MAC addresses using line-by-line parsing
• Returns a map of interface names to PortAttr structs containing ofport and MAC address for each interface
• Includes DumpPortMapping function variant to fetch port information for a single interface by name
• Validates ofport range (0-65535) and MAC address format, handling empty output and malformed lines gracefully
• Includes comprehensive test coverage with multiple test cases covering all scenarios

[yrkurapati]

Squashed into a single commit.

• Hope this would pass: https://github.com/digitalocean/go-openvswitch/actions/runs/19481221665/job/55752912890

[jcooperdo]

wouldn't a regex be much nicer for this?

[yrkurapati]

We did move from regexp
#141 (comment)

I did observe the existing code (table, flow, PortStats all use strings)

[jcooperdo]

Github links to comments that have been resolved don't show what you are trying to link. Could you quote the thread you're referencing?

[yrkurapati]

Could you follow semantics similar to parseEach() and define your own parseEachPort() or something like that, instead of regexp?

showPrefix =[]byte("OFPT_FEATURES_REPLY")

[yrkurapati]

@jcooperdo when you have time... ty!

[yrkurapati]

Converted this PR to a draft. After discussing with the team, we've decided to use the existing ovs-ofctl dump-ports approach (same method used by hvflowd) instead of implementing a new API with ovs-ofctl show.