Merge branch 'nexthop-various-fixes'

Ido Schimmel says:

====================
nexthop: Various fixes

This series contains various fixes for the nexthop code. The bugs were
uncovered during the development of resilient nexthop groups.

Patches #1-#2 fix the error path of nexthop_create_group(). I was not
able to trigger these bugs with current code, but it is possible with
the upcoming resilient nexthop groups code which adds a user
controllable memory allocation further in the function.

Patch #3 fixes wrong validation of netlink attributes.

Patch #4 fixes wrong invocation of mausezahn in a selftest.
====================

Link: https://lore.kernel.org/r/20210107144824.1135691-1-idosch@idosch.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>