fix(i2p): link boost_filesystem + boost_system (i2pd uses boost::filesystem)

libi2pd.a references boost::filesystem::detail::status, exists,
create_directories, etc. These are in boost_filesystem, which the
I2P link section was missing. Added Boost::filesystem and
Boost::system.

src/CMakeLists.txt

@@ -246,6 +246,7 @@ if(USE_I2P_EMBEDDED)
         "${I2P_SOURCE_ROOT}/libi2pdclient.a"
         "${I2P_SOURCE_ROOT}/libi2pdlang.a"
         Boost::program_options Boost::thread Boost::chrono
+        Boost::filesystem Boost::system
         OpenSSL::SSL OpenSSL::Crypto
         ZLIB::ZLIB
     )