lib: set: support port ranges in set elements

[ChatchawanIllyes]

Summary

Implements port ranges in set elements (#562).

bf_set_add_elem_raw() now recognises range syntax (START-END) in a set
element's components and expands it into individual set elements. For example:

(tcp.dport) in { 11; 22; 33-44 }

produces a set containing { 11, 22, 33, 34, …, 44 } (14 elements).

Range detection reuses the BF_MATCHER_RANGE parsing that already backs the
standalone range matcher operator — a component is treated as a range only
when the token contains a - and the component's matcher type registers
BF_MATCHER_RANGE ops. This scopes the feature to the matcher types that
already support ranges (ports today) without hardcoding anything port-specific,
and non-range / multi-component parsing is unchanged.

Behaviour

• Each value in [start, end] is expanded into its own element and inserted
  into the set's hashset, deduplicated like any other element.
• Expanded values are re-parsed through the existing single-value
  (BF_MATCHER_IN) path, so their in-memory representation is byte-identical to
  an element written as a plain value.
• Range bounds are validated by the existing _bf_parse_l4_port_range():
  both bounds must be valid decimal ports <= 65535, and start <= end.
  44-33, 33-, and -44 are rejected.

Scope / limitations

A couple of things are intentionally left out to keep this a minimal, focused
change — flagging them for maintainer input:

• Printing is unchanged. Expanded ranges are printed element-by-element,
  not re-factored back into a START-END range. This is the open question
  raised in Port range in sets #562; happy to add range factorization on ruleset get in a
  follow-up if that's the preferred direction.
• One ranged component per element. A set element with more than one ranged
  component (e.g. (tcp.sport, tcp.dport) in { 1-2, 3-4 }) returns -EINVAL
  rather than performing a Cartesian expansion. This avoids surprising blow-up
  in element count; can revisit if Cartesian expansion is wanted.

A note on element separators

The issue's example is written as { 11, 22, 33-44 }, but bpfilter separates
set elements with ; and components within an element with ,
(e.g. { 80; 443 } vs (ip4.daddr, tcp.sport) in { 1.2.3.4, 80 }). So the
range form is { 11; 22; 33-44 }. This PR does not change the grammar, so the
comma-separated form from the issue's example still parses as multiple
components. If treating , as an element separator for single-component sets
is desired, that's a separate grammar change and I'm glad to take it on
separately.

Tests

Added unit tests in tests/unit/libbpfilter/set.c:

• single-component range expansion ({11; 22; 33-44} → 14 elements)
• range boundaries (0-1, degenerate 65535-65535)
• invalid ranges (44-33, 33-, -44)
• a range in one component of a two-component key ({1.2.3.4, 80-82} → 3)
• ranges in both components of an element (rejected)

All unit.libbpfilter.set tests pass (28/28).

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[qdeslandes]

Hi, could you please disclose if/how much AI has been used for this work? Thank you.

[ChatchawanIllyes]

Hi, could you please disclose if/how much AI has been used for this work? Thank you.

Hey there, only used AI for two things: drafting the unit tests in tests/unit/libbpfilter/set.c, and writing up the PR description.

I reviewed both, and ran the test suite locally (unit.libbpfilter.set, 28/28) to confirm the cases and checked the tests actually cover what they say they do.