Merge branch 'vsock-fix-so_zerocopy-on-accept-ed-vsocks'

Michal Luczaj says:

====================
vsock: Fix SO_ZEROCOPY on accept()ed vsocks

vsock has its own handling of setsockopt(SO_ZEROCOPY). Which works just
fine unless socket comes from a call to accept(). Because
SOCK_CUSTOM_SOCKOPT flag is missing, attempting to set the option always
results in errno EOPNOTSUPP.
====================

Link: https://patch.msgid.link/20251229-vsock-child-sock-custom-sockopt-v2-0-64778d6c4f88@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>