WIP update to nrfxlib v1.4.2

[Wassasin]

This MR updates nrfxlib to v1.4.2, which is the latest stable version. v1.5.0 is almost released, but will prove to be a bigger albeit more promising update. I required this update due to the better socket connection establishment implementation in the newer bsdlib.

Note that temporarily I include my own fork of nrfxlib-sys, which I updated without being aware of the previous efforts by @jonathanpallant. Once nrf-rs/nrfxlib-sys#2 gets merged and released I'll change this merge request to point to the canonical one again. One minor issue is that this new nrfxlib-sys requires nightly, until -Zfeatures=host_dep ends up in stable. However that should not be a blocking issue for this merge request.

The changes required to update this library (afaik) are as follows:

• socket creation is more strict, requiring the Datagram type for At sockets. (since bsdlib 0.6.2) Therefor socket type None is no longer an appropriate value.
• bsdlib init requires parameters detailing the memory block set aside for the library. Because nrfxlib does not implement having no traces, trace_on should always be true. Perhaps we should not give the option to the end user.
• the fields of nrf_pollfd got renamed upstream.
• linking to nrfxlib now requires strncpy, which I added and has been merged at Add strncpy. rust-embedded-community/tinyrlibc#2.

I also fixed a minor issue with debug logging NrfSockAddrIn objects. We could move that out of this MR if so desired.

[jonathanpallant]

Looks good to me. I'll try and get the -sys changes in ASAP, and then once this is updated, we're good to go.

[jonathanpallant]

I published v1.4.2 of nrfxlib-sys just now, so please give it a spin.

[jonathanpallant]

Hmm. I note that -sys only include the soft-float libs (eabi, not eabihf) so I should probably remove the eabihf Github Action.