tests: py: fix up udp csum fixup output

tests: py: fix up udp csum fixup output

Preceeding commit switched udp to use the inkernel csum parser, so tests
warn:

WARNING: line 7: 'add rule ip test-ip4 input iif "lo" udp checksum set 0':
'[ payload write reg 1 => 2b @ transport header + 6 csum_type 1 csum_off 6 csum_flags 0x0 ]' mismatches
'[ payload write reg 1 => 2b @ transport header + 6 csum_type 0 csum_off 0 csum_flags 0x1 ]'

Fixes: f89abfb4068d ("proto: use NFT_PAYLOAD_L4CSUM_PSEUDOHDR flag to mangle UDP checksum")
Signed-off-by: Florian Westphal <fw@strlen.de>