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 Name Job ID Coverage
  Build
passed build:aarch64 #368791
librem5

00:15:50

passed build:deb #368792
librem5:arm64

01:07:50