MSVC: Avoid use `htonl' since it requires linking with Winsock

No need external library (Ws2_32.lib) if we can easily implement it.
Error messages:

  gost_core.lib(gost_keyexpimp.obj) : error LNK2019: unresolved external symbol htonl referenced in function gost_kdftree2012_256
  gost.dll : fatal error LNK1120: 1 unresolved externals

Signed-off-by: Vitaly Chikunov <vt@altlinux.org>