configs/avenger96_defconfig: linux build needs host-openssl
Fixes the gitlab build:
https://gitlab.com/buildroot.org/buildroot/-/jobs/1019385566/
HOSTCC scripts/extract-cert
scripts/extract-cert.c:21:25: fatal error: openssl/bio.h: No such file or directory
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>