fix ifa->ifa_addr nullptr

[qingyan01]

What type of PR is this?

bug

What problem(s) does this PR solve?

How do you solve it?

Special notes for your reviewer, ex. impact of this fix, design document, etc:

Checklist:

Tests:

• Unit test(positive and negative cases)
• Function test
• Performance test
• N/A

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• Documentation affected (Please add the label if documentation needs to be modified.)
• Incompatibility (If it breaks the compatibility, please describe it and add the label.）
• If it's needed to cherry-pick (If cherry-pick to some branches is required, please label the destination version(s).)
• Performance impacted: Consumes more CPU/Memory

Release notes:

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ex. Fixed the bug .....

[dutor]

LGTM.

Thanks for the fix.