ustream-ssl-wolfssl: add missing openssl dependency

`ustream-ssl` still needs `openssl` as a build input if it is built
against `wolfssl` (see [1]). I haven't deciphered the build setup
entirely, but from the respective CMake declarations, it looks like
the library still won't be linked against `openssl` if it is built
against `wolfssl` (see the `SET(SSL_LIB ...)` declarations), so I
guess `openssl` is solely needed for some header definitions.

[1]: https://git.openwrt.org/?p=project/ustream-ssl.git;a=blob;f=CMakeLists.txt;h=2de65905a40d8893155877a2b0894bcedec56f39;hb=HEAD#l24

pkgs/development/libraries/ustream-ssl/default.nix

@@ -1,4 +1,12 @@
-{ stdenv, lib, fetchgit, cmake, pkg-config, libubox-nossl, ssl_implementation }:
+{ stdenv
+, lib
+, fetchgit
+, cmake
+, pkg-config
+, libubox-nossl
+, ssl_implementation
+, additional_buildInputs ? [ ]
+}:
 
 stdenv.mkDerivation {
   pname = "ustream-ssl";
@@ -21,7 +29,7 @@ stdenv.mkDerivation {
   cmakeFlags = [ "-D${lib.toUpper ssl_implementation.pname}=ON" ];
 
   nativeBuildInputs = [ cmake pkg-config ];
-  buildInputs = [ ssl_implementation ];
+  buildInputs = [ ssl_implementation ] ++ additional_buildInputs;
 
   passthru = {
     inherit ssl_implementation;

pkgs/top-level/all-packages.nix

@@ -20955,7 +20955,7 @@ with pkgs;
 
   ustream-ssl = callPackage ../development/libraries/ustream-ssl { ssl_implementation = openssl; };
 
-  ustream-ssl-wolfssl = callPackage ../development/libraries/ustream-ssl { ssl_implementation = wolfssl; };
+  ustream-ssl-wolfssl = callPackage ../development/libraries/ustream-ssl { ssl_implementation = wolfssl; additional_buildInputs = [ openssl ]; };
 
   ustream-ssl-mbedtls = callPackage ../development/libraries/ustream-ssl { ssl_implementation = mbedtls_2; };