test: use IP_PORTRANGE_HIGH on FreeBSD for dynamic port allocation

On FreeBSD, the default ephemeral port range (10000-65535) overlaps
with the test framework's static port range (11000-26000), causing
intermittent "address already in use" failures when tests use dynamic
port allocation (port=0).

Add a helper function that sets the IP_PORTRANGE/IPV6_PORTRANGE socket
option to IP_PORTRANGE_HIGH before binding, which requests ports from
the high range (49152-65535) instead. This range does not overlap with
the test framework's static ports.

Constants from FreeBSD's netinet/in.h and netinet6/in6.h:
- IP_PORTRANGE = 19 (for IPv4 sockets)
- IPV6_PORTRANGE = 14 (for IPv6 sockets)
- IP_PORTRANGE_HIGH = 1

Fixes: bitcoin/bitcoin#34331

Co-Authored-By: Vasil Dimov <vd@FreeBSD.org>
Co-Authored-By: MarcoFalke <*~=\`'#}+{/-|&$^_@721217.xyz>

test/functional/test_framework/socks5.py

@@ -11,7 +11,8 @@ import queue
 import logging
 
 from .netutil import (
-    format_addr_port
+    format_addr_port,
+    set_ephemeral_port_range,
 )
 
 logger = logging.getLogger("TestFramework.socks5")
@@ -202,6 +203,10 @@ class Socks5Server():
         self.conf = conf
         self.s = socket.socket(conf.af)
         self.s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        # When using dynamic port allocation (port=0), ensure we don't get a
+        # port that conflicts with the test framework's static port range.
+        if conf.addr[1] == 0:
+            set_ephemeral_port_range(self.s)
         self.s.bind(conf.addr)
         # When port=0, the OS assigns an available port. Update conf.addr
         # to reflect the actual bound address so callers can use it.