Add new bpf_xdp_adjust_meta to docs/kernel-versions.md

Also adjust the order of helper functions.
diff --git a/docs/kernel-versions.md b/docs/kernel-versions.md
index 4985adc..135b946 100644
--- a/docs/kernel-versions.md
+++ b/docs/kernel-versions.md
@@ -131,6 +131,8 @@
 `BPF_FUNC_map_update_elem()` | 3.19 | [d0003ec01c66](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d0003ec01c667b731c139e23de3306a8b328ccf5)
 `BPF_FUNC_perf_event_output()` | 4.4 | [a43eec304259](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=a43eec304259a6c637f4014a6d4767159b6a3aa3)
 `BPF_FUNC_perf_event_read()` | 4.3 | [35578d798400](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=35578d7984003097af2b1e34502bc943d40c1804)
+`BPF_FUNC_perf_event_read_value()` | 4.15 | [908432ca84fc](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=908432ca84fc229e906ba164219e9ad0fe56f755)
+`BPF_FUNC_perf_prog_read_value()` | 4.15 | [4bebdc7a85aa](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4bebdc7a85aa400c0222b5329861e4ad9252f1e5)
 `BPF_FUNC_probe_read()` | 4.1 | [2541517c32be](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=2541517c32be2531e0da59dfd7efc1ce844644f5)
 `BPF_FUNC_probe_read_str()` | 4.11 | [a5e8c07059d0](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=a5e8c07059d0f0b31737408711d44794928ac218)
 `BPF_FUNC_probe_write_user()` | 4.8 | [96ae52279594](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=96ae52279594470622ff0585621a13e96b700600)
@@ -159,5 +161,4 @@
 `BPF_FUNC_tail_call()` | 4.2 | [04fd61ab36ec](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=04fd61ab36ec065e194ab5e74ae34a5240d992bb)
 `BPF_FUNC_trace_printk()` | 4.1 | [9c959c863f82](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=9c959c863f8217a2ff3d7c296e8223654d240569)
 `BPF_FUNC_xdp_adjust_head()` | 4.10 | [17bedab27231](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=17bedab2723145d17b14084430743549e6943d03)
-`BPF_FUNC_perf_event_read_value()` | 4.15 | [908432ca84fc](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=908432ca84fc229e906ba164219e9ad0fe56f755)
-`BPF_FUNC_perf_prog_read_value()` | 4.15 | [4bebdc7a85aa](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4bebdc7a85aa400c0222b5329861e4ad9252f1e5)
+`BPF_FUNC_xdp_adjust_meta()` | 4.15 | [de8f3a83b0a0](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=de8f3a83b0a0fddb2cf56e7a718127e9619ea3da)