LU-13004 lnet: discard kvec option from lnet_libmd.

LU-13004 lnet: discard kvec option from lnet_libmd.

The 'struct kvec' field in 'struct lnet_libmd' is no longer set - the
memory is always presented as pages.  So remove that option and the
union that contained iov and kiov.

Rename md_iov.kiov to md_kiov.
Discard all code that made use of md_iov.iov.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ic74a496c4c3df786d7fc194a1ad758c4daccd819
Reviewed-on: https://review.whamcloud.com/37843
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>