LU-17832 gni: build should not collapse extra symbols

LU-17832 gni: build should not collapse extra symbols

cray-obs spec files (ari,gem,dmp) define:
   KBUILD_EXTRA_SYMBOLS and GNICPPFLAGS

When building kgnilnd the environment variable needs to be passed
through to make.

HPE-bug-id: LUS-12269
Test-Parameters: trivial
Fixes: 8b1d2a72f1 ("LU-16967 build: Add in-kernel-ko2iblnd driver")
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: Icc7ac33138300bf3836082a014daf580a1632436
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55052
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Patrick Farrell <patrick.farrell@oracle.com>
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>