skmsg: Fix wrong last sg check in sk_msg_recvmsg()

In the Linux kernel, the following vulnerability has been resolved:

skmsg: Fix wrong last sg check in sk_msg_recvmsg()

Fix one kernel NULL pointer dereference as below:

[ 224.462334] Call Trace:

[ 224.462394] __tcp_bpf_recvmsg+0xd3/0x380

[ 224.462441] ? sock_has_perm+0x78/0xa0

[ 224.462463] tcp_bpf_recvmsg+0x12e/0x220

[ 224.462494] inet_recvmsg+0x5b/0xd0

[ 224.462534] __sys_recvfrom+0xc8/0x130

[ 224.462574] ? syscall_trace_enter+0x1df/0x2e0

[ 224.462606] ? __do_page_fault+0x2de/0x500

[ 224.462635] __x64_sys_recvfrom+0x24/0x30

[ 224.462660] do_syscall_64+0x5d/0x1d0

[ 224.462709] entry_SYSCALL_64_after_hwframe+0x65/0xca

In commit 9974d37ea75f ("skmsg: Fix invalid last sg check in

sk_msg_recvmsg()"), we change last sg check to sg_is_last(),

but in sockmap redirection case (without stream_parser/stream_verdict/

skb_verdict), we did not mark the end of the scatterlist. Check the

sk_msg_alloc, sk_msg_page_add, and bpf_msg_push_data functions, they all

do not mark the end of sg. They are expected to use sg.end for end

judgment. So the judgment of '(i != msg_rx->sg.end)' is added back here.