Test randomly selected client port for availabilty in sslrecords test

Encountered this error in a pr today:
https://github.com/openssl/openssl/actions/runs/15418713146/job/43387767612

===
Proxy started on port [::1]:56662
Engine "ossltest" set.
Using default temp DH parameters
ACCEPT [::1]:59189
Server responds on [::1]:59189
Engine "ossltest" set.
C0774F02907F0000:error:80000062:system library:BIO_bind:Address already in use:crypto/bio/bio_sock2.c:240:calling bind()
C0774F02907F0000:error:10000075:BIO routines:BIO_bind:unable to bind socket:crypto/bio/bio_sock2.c:242:
connect:errno=98
===

Its occuring because we randomly select a port to use for our client
connection in the sslrecords test.  Thats usually fine, but sometimes,
we get unlucky and pick a port thats already in use.  This presents as
random failures in our CI on this test.

So lets try harden ourselves against it.  When creating the client
connection, test the randomly selected port by trying to bind to it via
a call to IO::Socket::IP->new(). If that fails, try a different port
number, until we get one that works.  If it works, use that port in the
assignment for the clients local port value.

Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27752)

util/perl/TLSProxy/Proxy.pm

@@ -93,6 +93,7 @@ sub new_dtls {
 
 sub init
 {
+    require IO::Socket::IP;
     my $class = shift;
     my ($filter,
         $execute,
@@ -100,10 +101,44 @@ sub init
         $debug,
         $isdtls) = @_;
 
+    my $test_client_port;
+
+    # Sometimes, our random selection of client ports gets unlucky
+    # And we randomly select a port thats already in use.  This causes
+    # this test to fail, so lets harden ourselves against that by doing
+    # a test bind to the randomly selected port, and only continue once we
+    # find a port thats available.
+    my $test_client_addr = $have_IPv6 ? "[::1]" : "127.0.0.1";
+    my $found_port = 0;
+    for (my $i = 0; $i <= 10; $i++) {
+        $test_client_port = 49152 + int(rand(65535 - 49152));
+        my $test_sock;
+        if ($have_IPv6) {
+            $test_sock = IO::Socket::IP->new(Family => AF_INET6,
+                                             LocalPort => $test_client_port,
+                                             LocalAddr => $test_client_addr);
+        } else {
+            $test_sock = IO::Socket::IP->new(Family => AF_INET,
+                                             LocalPort => $test_client_port,
+                                             LocalAddr => $test_client_addr);
+        }
+        if ($test_sock) {
+            $found_port = 1;
+            $test_sock->close();
+            print "Found available client port ${test_client_port}\n";
+            last;
+        }
+        print "Port ${test_client_port} in use.  Trying again\n";
+    }
+  
+    if ($found_port == 0) {
+        die "Unable to find usable port for TLSProxy";
+    }
+
     my $self = {
         #Public read/write
-        proxy_addr => $have_IPv6 ? "[::1]" : "127.0.0.1",
+        proxy_addr => $test_client_addr,
-        client_addr => $have_IPv6 ? "[::1]" : "127.0.0.1",
+        client_addr => $test_client_addr,
         filter => $filter,
         serverflags => "",
         clientflags => "",
@@ -114,7 +149,7 @@ sub init
         #Public read
         isdtls => $isdtls,
         proxy_port => 0,
-        client_port => 49152 + int(rand(65535 - 49152)),
+        client_port => $test_client_port,
         server_port => 0,
         serverpid => 0,
         clientpid => 0,