librem5_defconfig: Enable netfilter-related options

Main motivation was to fix errors reported by NetworkManager
while enabling WiFi hotspot - but also added more options after
consulting Debian's kernel config, which has them enabled.
2 jobs for nf in 67 minutes and 51 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #368791
librem5
build:aarch64

00:15:50

passed #368792
librem5:arm64
build:deb

01:07:50