Make the DECT-2020 NR+ libmodem.a available as a feature#16

chrysn wants to merge 2 commits intonrf-rs:developnrf-rs/nrfxlib-sys:developfrom

chrysn-pull-requests:test-dect-bischrysn-pull-requests/nrfxlib-sys:test-dect-bisCopy head branch name to clipboard