UDP recv works in Python console, does not work when executed as python3 exploit.py

The following issue was reproducible on the latest Docker image, on macOS and in Kali.

```
from pwn import *
context.log_level = 'debug'
l = listen(typ='udp')
r = udp('localhost', l.lport)
r.send(b'test')
l.recv(timeout=4)
```

If this script is started inside python shell, all is good, l.recv receives hello.

```
Python 3.9.2 (default, Feb 28 2021, 17:03:44)
[GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from pwn import *
>>> context.log_level = 'debug'
>>> l = listen(typ='udp')
[x] Trying to bind to :: on port 0
[x] Trying to bind to :: on port 0: Trying ::
[+] Trying to bind to :: on port 0: Done
[x] Waiting for connections on :::34099
>>> r = udp('localhost', l.lport)
[x] Opening connection to localhost on port 34099
[x] Opening connection to localhost on port 34099: Trying ::1
[+] Opening connection to localhost on port 34099: Done
>>> r.send(b'test')
[DEBUG] Sent 0x4 bytes:
b'test'
>>> l.recv(timeout=4)[+] Waiting for connections on :::34099: Got connection from ::1 on port 40984

b'test'
>>>
```

But once the code is saved as a python file and run with python3 exploit.py, l.recv is not receiving anything.

```
[+] Trying to bind to :: on port 0: Done
[+] Waiting for connections on :::55214: Got connection from ::1 on port 35994
[+] Opening connection to localhost on port 55214: Done
[DEBUG] Sent 0x4 bytes:
b'test'
[*] Closed connection to localhost port 55214
[*] Closed connection to ::1 port 35994
```

strace of the incorrect run
```
write(1, "[\33[1m\33[31mDEBUG\33[m] Sent 0x4 byt"..., 39[DEBUG] Sent 0x4 bytes:
) = 39
getpWaiting for connections on :::36419: Got connection from ::1 on port 48863
[+] e(1, " b'test'\33[K\n", 15 b'test'
) = 15
poll([{fd=5, events=POLLOUT}], 1, 1048576000) = 1 ([{fd=5, revents=POLLOUT}])
) = 4
ioctl(1, TCGETS, {B38400 opost isig -icanon -echo ...}) = 0
ioctl(1, TCGETS, {B38400 opost isig -icanon -echo ...}) = 0
ioctl(1, SNDCTL_TMR_STOP or TCSETSW, {B38400 opost isig icanon echo ...}) = 0
ioctl(1, TCGETS, {B38400 opost isig icanon echo ...}) = 0
close(5) = 0
getpid() = 65307
write(1, "\33[?12l\33[?25h\33[?1l\33> \10[\33[1m\33[34m*"..., 82[*] Closed connection to localhost port 36419
) = 82
close(4) = 0
getpid() = 65307
write(1, "[\33[1m\33[34m*\33[m] Closed connectio"..., 55[*] Closed connection to ::1 port 48863
) = 55
lseek(3, 0, SEEK_CUR) = 0
rt_sigaction(SIGINT, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f26f1931140}, {sa_handler=0x6402c0, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f26f1931140}, 8) = 0
rt_sigaction(SIGCONT, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f26f1931140}, {sa_handler=0x6402c0, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f26f1931140}, 8) = 0
rt_sigaction(SIGTSTP, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f26f1931140}, {sa_handler=0x6402c0, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f26f1931140}, 8) = 0
rt_sigaction(SIGWINCH, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f26f1931140}, {sa_handler=0x6402c0, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f26f1931140}, 8) = 0
lseek(3, 0, SEEK_CUR) = 0
lseek(3, 0, SEEK_CUR) = 0
close(3) = 0

```

Start by tracing the listen(typ='udp'), udp('localhost', l.lport), and l.recv(timeout=4) entry points and compare their behavior in an interactive console and a standalone script. Reproduce the provided example, then verify that the standalone script receives b'test' without changing the example's expected UDP behavior.

Written by the indexing model from the issue text.