net: context: Move asserts to proper place
net: context: Move asserts to proper place

net_context local sin/sin6 addresses are used only
when input src is not available. So ASSERT should
be inside if block.

Signed-off-by: Ravi kumar Veeramally <406c082aeb452858c41b213a757768e1c1dff29e@linux.intel.com>

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