LU-15962 build: add in-kernel Module.symvers to symbol path

LU-15962 build: add in-kernel Module.symvers to symbol path

After building Lustre with in-kernel OFED, installing
ko2iblnd module hit the following errors:

ko2iblnd: disagrees about version of symbol __ib_alloc_pd
ko2iblnd: Unknown symbol __ib_alloc_pd (err -22)
ko2iblnd: disagrees about version of symbol rdma_resolve_addr
ko2iblnd: Unknown symbol rdma_resolve_addr (err -22)

Those exported symbols are contained in in-kernel Module.symvers,
which should be added to the symbol path KBUILD_EXTRA_SYMBOLS.

Lustre-change: https://review.whamcloud.com/47699
Lustre-commit: TBD (from c4ba25c4c3ddbb66ddb5a5f0e2c87140a541ec3b)

Test-Parameters: trivial

Change-Id: Ic30caa7079af00a452ea24e7e982a856874af702
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/47688
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>