fix: hash only source IP for consistent hash policy

[areycruzer]

What type of PR is this?

/kind bug

What this PR does / why we need it:

The consistent-hash load balancer's useSourceIp mode hashed the full RemoteAddr() string (IP:port) instead of only the source IP. Because client source ports are ephemeral, the same client could be routed to a different backend on every new connection, defeating session stickiness and violating the Istio ConsistentHashLB.useSourceIp contract.

This change extracts only the host from the source address before hashing:

• IPv4 and IPv6 (bracketed) addresses are handled via net.SplitHostPort, with a fallback for addresses without a port.
• Empty or missing source addresses now return a descriptive error instead of hashing an ambiguous key.
• The existing netConn.RemoteAddr() fallback behavior is preserved.

Regression tests prove the same source IP with different ephemeral ports now selects the same endpoint, for both IPv4 and IPv6, plus error cases for empty/malformed addresses.

Which issue(s) this PR fixes:

Fixes #587

Special notes for your reviewer:

Verified with go test ./pkg/loadbalancer -count=1 under Go 1.19 on Linux (the repository's pinned toolchain).

Does this PR introduce a user-facing change?:

Fixed consistent-hash load balancing with `useSourceIp`: the hash key now uses only the client source IP, so connections from the same client consistently reach the same backend regardless of ephemeral source port.

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This pull-request has been approved by: areycruzer
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[kubeedge-bot]

Welcome @areycruzer! It looks like this is your first PR to kubeedge/edgemesh 🎉