zdtm: Skip socket_udplite test when kernel lacks UDPLITE

Kernel 7.1 removed IPPROTO_UDPLITE support. Add a checkskip
script that probes for a UDPLITE socket and skips the test
with EPROTONOSUPPORT instead of failing.

Assisted-by: Claude Code (claude-opus-4-6):claude-opus-4-6@default
Signed-off-by: Adrian Reber <areber@redhat.com>

test/zdtm/static/socket_udplite.checkskip

@@ -0,0 +1,15 @@
+#!/usr/bin/env python3
+# IPPROTO_UDPLITE was removed in kernel 7.1, skip the test if the
+# protocol is not available.
+import socket
+import errno
+
+try:
+	socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDPLITE).close()
+except OSError as e:
+	if e.errno == errno.EPROTONOSUPPORT:
+		print("UDPLITE is not supported by this kernel.")
+		exit(1)
+	raise
+
+exit(0)