WASM extension crashes on Big-endian machine

[knm3000]

Rust WASM extension https://github.com/maistra/header-append-filter crashes on s390x:

2021-09-07T17:11:51.327902Z     error   envoy wasm      Function: proxy_on_configure failed: Uncaught RuntimeError: memory access out of bounds
Proxy-Wasm plugin in-VM backtrace:
  0:  0x1aa1 - _ZN10serde_json5value2de77_$LT$impl$u20$serde..de..Deserialize$u20$for$u20$serde_json..value..Value$GT$11deserialize17hb4f81bdbc27fce53E.llvm.10413096860284390022
  1:  0x17fa - _ZN10serde_json2de10from_slice17had30ef6d3adf186fE
  2:  0x64a0 - _ZN97_$LT$header_append_filter..HeaderAppendRootContext$u20$as$u20$proxy_wasm..traits..RootContext$GT$12on_configure17h5f96597ce1e2a394E
  3:  0xfffa - _ZN10proxy_wasm10dispatcher10Dispatcher12on_configure17h4a9f78f0de537835E
  4:  0x1220a - proxy_on_configure
2021-09-07T17:11:51.327927Z     error   envoy wasm      Wasm VM failed Failed to configure base Wasm plugin
2021-09-07T17:11:51.328771Z     critical        envoy wasm      Plugin configured to fail closed failed to load