Fix Deadlock in Flush Function Due to ENOBUFS

[patryk4815]

Hi.
This PR resolves a issue in the Flush function, where a deadlock occurs when the kernel returns an ENOBUFS error.
This issue has been observed in our production 🙃 (cc: @Ignatella )

Changes:

• Fix deadlock in Flush function
• Added test to simulate the issue using a reduced read/write buffer, ensuring that the fix works correctly and prevents regressions

Debugger:

Switched from 56906 to 1 (thread 2855201)
(dlv) bt
0  0x000000000043de2e in runtime.gopark
    at runtime/proc.go:399
1  0x00000000004368b7 in runtime.netpollblock
    at runtime/netpoll.go:564
2  0x0000000000468425 in internal/poll.runtime_pollWait
    at runtime/netpoll.go:343
3  0x00000000004dbe67 in internal/poll.(*pollDesc).wait
    at internal/poll/fd_poll_runtime.go:84
4  0x00000000004e1fca in internal/poll.(*pollDesc).waitRead
    at internal/poll/fd_poll_runtime.go:89
5  0x00000000004e1fca in internal/poll.(*FD).RawRead
    at internal/poll/fd_unix.go:708
6  0x00000000004eb20a in os.(*rawConn).Read
    at os/rawconn.go:31
7  0x000000000079a56b in syscall.RawConn.Read-fm
    at <autogenerated>:1
8  0x0000000000798c49 in github.com/mdlayher/socket.rwT[go.shape.struct { github.com/mdlayher/socket.n int; github.com/mdlayher/socket.oobn int; github.com/mdlayher/socket.recvflags int; github.com/mdlayher/socket.from golang.org/x/sys/unix.Sockaddr }]
    at github.com/mdlayher/[email protected]/conn.go:795
9  0x00000000007984f2 in github.com/mdlayher/socket.readT[go.shape.struct { github.com/mdlayher/socket.n int; github.com/mdlayher/socket.oobn int; github.com/mdlayher/socket.recvflags int; github.com/mdlayher/socket.from golang.org/x/sys/unix.Sockaddr }]
    at github.com/mdlayher/[email protected]/conn.go:666
10  0x0000000000791eb4 in github.com/mdlayher/socket.(*Conn).Recvmsg
    at github.com/mdlayher/[email protected]/conn.go:572
11  0x000000000079f3f6 in github.com/mdlayher/netlink.(*conn).Receive
    at github.com/mdlayher/[email protected]/conn_linux.go:130
12  0x000000000079d9c2 in github.com/mdlayher/netlink.(*Conn).receive
    at github.com/mdlayher/[email protected]/conn.go:279
13  0x000000000079d747 in github.com/mdlayher/netlink.(*Conn).lockedReceive
    at github.com/mdlayher/[email protected]/conn.go:238
14  0x000000000079d62d in github.com/mdlayher/netlink.(*Conn).Receive
    at github.com/mdlayher/[email protected]/conn.go:231
15  0x00000000007ac35e in github.com/google/nftables.receiveAckAware
    at github.com/google/[email protected]/conn.go:94
16  0x00000000007acec5 in github.com/google/nftables.(*Conn).Flush
.......
    at runtime/proc.go:267
24  0x000000000046dbc1 in runtime.goexit
    at runtime/asm_amd64.s:1650
 
(dlv) frame 16

(dlv) p errs
error(*errors.joinError) *{
	errs: []error len: 1, cap: 1, [
		...,
	],}

(dlv) p errs.errs
[]error len: 1, cap: 1, [
	*github.com/mdlayher/netlink.OpError {
		Op: "receive",
		Err: error(*os.SyscallError) ...,
		Message: "",
		Offset: 0,},
]

(dlv) p errs.errs[0]
error(*github.com/mdlayher/netlink.OpError) *{
	Op: "receive",
	Err: error(*os.SyscallError) *{
		Syscall: "recvmsg",
		Err: error(syscall.Errno) *(*error)(0xc000034090),},
	Message: "",
	Offset: 0,}

(dlv) p errs.errs[0].Err
error(*os.SyscallError) *{
	Syscall: "recvmsg",
	Err: error(syscall.Errno) ENOBUFS (105),}

(dlv) p errs.errs[0].Err.Err
error(syscall.Errno) ENOBUFS (105)

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