ANDROID: add flags variable back to struct proto_ops

In commit a3025359 ("net: remove cmsg restriction from io_uring
based send/recvmsg calls") the flags variable was removed from struct
proto_ops as it is no longer needed.

But the ABI signatures break, so put it back to preserve this, there's
no functional change here.

Bug: 161946584
Bug: 268174392
Fixes: a3025359 ("net: remove cmsg restriction from io_uring based send/recvmsg calls")
Change-Id: Ic6a868f038701a61c993e18b44cdd8ec8b0a4d58
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>