tcp: add SO_PEEK_OFF socket option tor TCPv6

When doing further testing of the recently added SO_PEEK_OFF feature
for TCP I realized I had omitted to add it for TCP/IPv6.

I do that here.

Fixes: 05ea4916 ("tcp: add support for SO_PEEK_OFF socket option")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Tested-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Link: https://patch.msgid.link/20240828183752.660267-2-jmaloy@redhat.com


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