socket.read() freezes when 4096 or multiple of 4096 bytes in socket for readout

Tested on Linux and MacOS and manifests on both.

Below is the reproduction pattern. Just copy/paste to SocketsTests.swift and run tests.

`

func testReadX4096BytesIssue() {

var data = Data()

do {

// Launch the server helper...
launchServerHelper(family: .unix)

// Need to wait for the server to come up...
#if os(Linux)
_ = Glibc.sleep(2)
#else
_ = Darwin.sleep(2)
#endif

// Create the signature...
let signature = try Socket.Signature(socketType: .stream, proto: .unix, path: path)!

// Create the socket...
let socket = try createHelper(family: .unix)

// Defer cleanup...
defer {
// Close the socket...
socket.close()
XCTAssertFalse(socket.isActive)
}

// Connect to the server helper...
try socket.connect(using: signature)
if !socket.isConnected {

fatalError("Failed to connect to the server...")
}

print("\nConnected to path: \(path)")
print("\tSocket signature: \(socket.signature!.description)\n")

_ = try readAndPrint(socket: socket, data: &data)

for count in [4095, 4097, 4096]
{
let hello = String(repeating: "a", count: count)
let bytesWritten = try socket.write(from: hello)

print("Wrote '\(bytesWritten)' bytes to socket...")

let response = try readAndPrint(socket: socket, data: &data)

XCTAssertNotNil(response)
XCTAssertEqual(response!, "Server response: \n\(hello)\n")
}
try socket.write(from: "QUIT")

print("Sent quit to server...")

// Need to wait for the server to go down before continuing...
#if os(Linux)
_ = Glibc.sleep(1)
#else
_ = Darwin.sleep(1)
#endif

} catch let error {

// See if it's a socket error or something else...
guard let socketError = error as? Socket.Error else {

print("Unexpected error...")
XCTFail()
return
}

print("testReadWriteUnix Error reported: \(socketError.description)")
XCTFail()
}
}

static var allTests = [
("testDefaultCreate", testDefaultCreate),
("testCreateIPV6", testCreateIPV6),
("testCreateUnix", testCreateUnix),
("testCreateUDP", testCreateUDP),
("testListen", testListen),
("testListenPort0", testListenPort0),
("testListenUnix", testListenUnix),
("testListenUDP", testListenUDP),
("testListenPort0UDP", testListenPort0UDP),
("testConnect", testConnect),
("testConnectTo", testConnectTo),
("testConnectToWithTimeout", testConnectToWithTimeout),
("testConnectToPath", testConnectToPath),
("testConnectPort0", testConnectPort0),
("testHostnameAndPort", testHostnameAndPort),
("testBlocking", testBlocking),
("testSetReadTimeout", testSetReadTimeout),
("testSetWriteTimeout", testSetWriteTimeout),
("testIsReadableWritableFail", testIsReadableWritableFail),
("testIsReadableWritable", testIsReadableWritable),
("testFDSetBitFields", testFDSetBitFields),
("testDomainSocketPath", testDomainSocketPath),
("testReadWrite", testReadWrite),
("testTruncateTCP", testTruncateTCP),
("testReadWriteUDP", testReadWriteUDP),
("testReadWriteUnix", testReadWriteUnix),
("testReadWriteUnix", testReadX4096BytesIssue),
]
}
`