LU-17342 o2ib: build without Module.symvers

LU-17342 o2ib: build without Module.symvers

When building against an external kernel tree, the
configure script fails if there isn't a Module.symvers
available. This prevents us from using the
'modules_prepare' make target on the kernel tree.
ko2iblnd.ko can be build even without Module.symvers.
Hence, downgrade this message from an error to a
warning.

Also, don't fail if ko2iblnd can't be built. Just
emit a warning.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I8bca7f945c753fdac3aa5d9889d3347613baf059
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53358
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>