npcap_sdk: add mingw support with workaround for unrecognized SAL

[Doekin]

Workaround for Unrecognized MSVC SAL Annotation _Post_invalid_

Problem

Npcap's introduction of specific SAL annotations in this commit has created compatibility issues with MinGW, which does not recognize the _Post_invalid_ annotation.

Possible Solutions

• Revert to a Previous Version: Use an earlier version of npcap that lacks these SAL annotations.
• Upgrade MinGW Toolchain: Switch to a newer MinGW version that #define _Post_invalid_ in sal.h. See the related MinGW commit.
• Wait for Next Npcap SDK Release: The upcoming npcap_sdk release is expected to resolve this issue, as mentioned in this discussion. However, it's worth noting that the last release was in 2022.