udp: seq_file: Helper function to match socket attributes

This is a preparatory commit to refactor code that matches socket
attributes in iterators to a helper function, and use it in the
proc fs iterator.

Signed-off-by: Aditi Ghag <aditi.ghag@isovalent.com>
Link: https://lore.kernel.org/r/20230519225157.760788-3-aditi.ghag@isovalent.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>