bcachefs-tools: don't assume modprobe is in the PATH

This was kind of non-obvious to figure out. See
https://github.com/koverstreet/bcachefs-tools/issues/521 upstream for
more information.

I don't know if there are downsides to making this package depend on
`kmod`.

pkgs/by-name/bc/bcachefs-tools/package.nix

@@ -6,6 +6,7 @@
   libuuid,
   libsodium,
   keyutils,
+  kmod,
   liburcu,
   zlib,
   libaio,
@@ -45,6 +46,9 @@ stdenv.mkDerivation (finalAttrs: {
   postPatch = ''
     substituteInPlace Makefile \
       --replace-fail "target/release/bcachefs" "target/${stdenv.hostPlatform.rust.rustcTargetSpec}/release/bcachefs"
+
+    substituteInPlace src/commands/mount.rs \
+      --replace-fail 'std::process::Command::new("modprobe")' 'std::process::Command::new("${lib.getExe' kmod "modprobe"}")'
   '';
 
   nativeBuildInputs = [