Merge branch 'selftests-net-fix-a-few-small-compiler-warnings'

Willem de Bruijn says:

====================
selftests/net: fix a few small compiler warnings

Observed a clang warning when backporting cmsg_sender.
Ran the same build against all the .c files under selftests/net.

This is clang-14 with -Wall
Which is what tools/testing/selftests/net/Makefile also enables.
====================

Link: https://lore.kernel.org/r/20231124171645.1011043-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>