LU-17877 lnet: export REGISTER_FUNC with EXPORT_SYMBOL_GPL

LU-17877 lnet: export REGISTER_FUNC with EXPORT_SYMBOL_GPL

This patch exports REGISTER_FUNC and UNREGISTER_FUNC
with EXPORT_SYMBOL_GPL to load GPL-licensed modules.

Test-Parameters: trivial

Change-Id: I3a0d4e2b27911af36e210692d28892590eb0371c
Signed-off-by: Rebanta Mitra <rmitra@nvidia.com>
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55217
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>