bpftools: strip path to the binary from prints

Otherwise meson's find_program() can get confused by the output;
now in case of systemd build:
meson.build:1059:16: ERROR: Invalid version of program, need 'bpftool' ['>= 5.6.0'] found '01'.

pkgs/os-specific/linux/bpftools/default.nix

···
     sha256 = "sha256-xDalSMcxLOb8WjRyy+rYle749ShB++fHH9jki9/isLo=";
   };
 
+  patches = [ ./strip-binary-name.patch ];
+
   nativeBuildInputs = [ python3 bison flex ];
   buildInputs = (if (lib.versionAtLeast version "5.20")
                  then [ libopcodes libbfd ]

pkgs/os-specific/linux/bpftools/strip-binary-name.patch

···
+Strip path to the binary from prints.
+
+I see no sense in including the full path in outputs like bpftool --version
+Especially as argv[0] may not include it, based on calling via $PATH or not.
+--- a/tools/bpf/bpftool/main.c
++++ b/tools/bpf/bpftool/main.c
+@@ -443 +443,7 @@
+-	bin_name = argv[0];
++	/* Strip the path if any. */
++	const char *bin_name_slash = strrchr(argv[0], '/');
++	if (bin_name_slash) {
++		bin_name = bin_name_slash + 1;
++	} else {
++		bin_name = argv[0];
++	}