Make code work using NSS in FIPS-mode

[msirringhaus]

This is part of an effort to make webRTC calls work under FIPS in Firefox. (See here and more specifically here)

How to test:

meson setup -Dcrypto-library=nss build
export NSS_FIPS=1
meson test -C build

Half the tests fail without this patch and all work with it (tests also work with unset NSS_FIPS).

PK11_ImportSymKey() is not allowed to be used under FIPS, but there can be a workaroud to still be able to import raw key material, by encrypting it first and then unwrapping it (which is in the end a NO-OP, but satisfies the API under FIPS).

[nils-ohlmeier]

Look good to me, but I think we need a review with crypto expertise like @bifurcation here.

[pabuhler]

@msirringhaus you can ignore the fuzzing test for now, but please fix the other failures so we can get a review and move forward. Thanks

[msirringhaus]

Sorry, I pushed to early and had to fix the formatting again.

[pabuhler]

Sorry, I pushed to early and had to fix the formatting again.

and I approved to quickly :)