Merge branch 'rtnetlink-honour-nlm_f_echo-flag-in-rtnl_-new-del-link'

Hangbin Liu says:

====================
rtnetlink: Honour NLM_F_ECHO flag in rtnl_{new, del}link

Netlink messages are used for communicating between user and kernel space.
When user space configures the kernel with netlink messages, it can set the
NLM_F_ECHO flag to request the kernel to send the applied configuration back
to the caller. This allows user space to retrieve configuration information
that are filled by the kernel (either because these parameters can only be
set by the kernel or because user space let the kernel choose a default
value).

The kernel has support this feature in some places like RTM_{NEW, DEL}ADDR,
RTM_{NEW, DEL}ROUTE. This patch set handles NLM_F_ECHO flag and send link
info back after rtnl_{new, del}link.
====================

Link: https://lore.kernel.org/r/20221028084224.3509611-1-liuhangbin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>