aya-ebpf: Add BPF_F_ADJ_ROOM_ENCAP_L2 "macro"

This function is needed to properly add a L2 header when using `bpf_skb_adjust_room` [1].
As it is originally a C macro, it isn't automatically generated in the `bindings` cratea

[1]: https://docs.ebpf.io/linux/helper-function/bpf_skb_adjust_room/

ebpf/aya-ebpf/src/lib.rs

@@ -113,6 +113,18 @@ mod intrinsics {
     }
 }
 
+/// Builds a flag for [`SkBuffContext::adjust_room`] that defines L2 encapsulation,
+/// using `len` as the inner MAC header length.
+///
+/// Equivalent to the [`BPF_F_ADJ_ROOM_ENCAP_L2`][uapi-bpf-adj-room-encap-l2] macro
+/// in the Linux user-space API.
+///
+/// [uapi-bpf-adj-room-encap-l2]: https://github.com/torvalds/linux/blob/v6.17/include/uapi/linux/bpf.h#L6181
+#[inline(always)]
+pub const fn bpf_f_adj_room_encap_l2(len: u64) -> u64 {
+    (len & bindings::BPF_ADJ_ROOM_ENCAP_L2_MASK as u64) << bindings::BPF_ADJ_ROOM_ENCAP_L2_SHIFT
+}
+
 /// Check if a value is within a range, using conditional forms compatible with
 /// the verifier.
 #[inline(always)]

xtask/public-api/aya-ebpf.txt

@@ -2991,4 +2991,5 @@ impl aya_ebpf::EbpfContext for aya_ebpf::programs::tracepoint::TracePointContext
 pub fn aya_ebpf::programs::tracepoint::TracePointContext::as_ptr(&self) -> *mut core::ffi::c_void
 impl aya_ebpf::EbpfContext for aya_ebpf::programs::xdp::XdpContext
 pub fn aya_ebpf::programs::xdp::XdpContext::as_ptr(&self) -> *mut core::ffi::c_void
+pub const fn aya_ebpf::bpf_f_adj_room_encap_l2(len: u64) -> u64
 pub fn aya_ebpf::check_bounds_signed(value: i64, lower: i64, upper: i64) -> bool