ipv4: accept u8 in IP_TOS ancillary data

In commit f02db315 ("ipv4: IP_TOS and IP_TTL can be specified as
ancillary data") Francesco added IP_TOS values specified as integer.

However, kernel sends to userspace (at recvmsg() time) an IP_TOS value
in a single byte, when IP_RECVTOS is set on the socket.

It can be very useful to reflect all ancillary options as given by the
kernel in a subsequent sendmsg(), instead of aborting the sendmsg() with
EINVAL after Francesco patch.

So this patch extends IP_TOS ancillary to accept an u8, so that an UDP
server can simply reuse same ancillary block without having to mangle
it.

Jesper can then augment
https://github.com/netoptimizer/network-testing/blob/master/src/udp_example02.c
to add TOS reflection ;)

Fixes: f02db315

 ("ipv4: IP_TOS and IP_TTL can be specified as ancillary data")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Francesco Fusco <ffusco@redhat.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>