devlink: move and rename devlink_dpipe_send_and_alloc_skb() helper

Since both dpipe and resource code is using this helper, in preparation
for code split to separate files, move
devlink_dpipe_send_and_alloc_skb() helper into netlink.c. Rename it on
the way.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20230828061657.300667-5-jiri@resnulli.us


Signed-off-by: Jakub Kicinski <kuba@kernel.org>