fix: add dhcp discover packet to linux swiftv2 to ensure mappings exist for dns

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Reason for Change:

In linux swiftv2, nslookup using the wireserver may fail in certain scenarios. The theory is that this is because the host does not have mappings/state for the dns on the secondary/delegated nics (eth1). To ensure that state is created, we send a dhcp discover packet through the delegated nic (eth1) so the mappings are created. Any offers returned are ignored.

Issue Fixed:

See above.

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• relevant PR labels added

Notes:
We assume that epInfo.IfName contains the actual interface name of the nic! The dhcp discover packet MUST get a successful offer or the add call will fail. If in swiftv2 we have multiple nics, we send the dhcp request for each one and all must succeed or the add call will fail. Ensure the ifName is in epInfo.ifName

Should affect Swiftv2 Linux only.
 
Reviewer(s):

• Code includes goroutines/synchronization (potential data races?)
• Verify indexing is correct/no possibility of panics/accessing out of bounds
• Code deals with sockets (verify all sockets always properly closed)

Tested:

• Swiftv2 linux create mt pod 1.6.5 cns (we do get a reply from the dhcp server), logs corroborate
• Attempt request with wrong mac address, we time out and error as expected
• Attempt request with wrong ifname, we time out and error as expected
• Context deadline error as expected if set context deadline to 0 sec
• Repro'd issue, then applied CNI fix, then recreated pod to issue dhcp request, and then I can contact dns via secondary nic as expected (previously I couldn't)

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