LU-10391 uapi: move out kernel only code.

LU-10391 uapi: move out kernel only code.

Userland doesn't use the new IPv6 function in the UAPI nidstr.h.
So move this to the kernel header lib-types.h. Normally this
wouldn't matter but the python wrappers break with the LUTF
project. With the move to Netlink in the future for the user land
API we shouldn't need these functions anyways.

Test-parameters: trivial
Change-Id: I2ac6d102d4575f639573253c21723d62ca08abc2
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/44844
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>