Dodo Nethub support (#445)

* added support for XNS networking via Dodo-Nethub

* NetHub connection now optional (only if -nh-host is given); released NetHub-related changes to 'ether.c' to the public domain

* Added file using-dodo-networking-with-maiko.md

Documentation for building and using the Dodo-networking addition to Maiko

* Added support for running Maiko unter cygwin/x86_64-x

* Migrate Addr68k/NativeAlignment{2,4} in Nethub code, move timer/async defines to platform.h

* added missing include <netinet/in.h> for FreeBSD

* updated 'compile-flags' with added flags

* splitted ether.c in 3 (_common, _sunos, _nethub)

* reworks/modifications for nbriggs' pull-request review comments

* addintional additions for nbriggs' pull-request review comments

* get the Lisp packet lengths with 'LispInt2CInt'

* renamed variables in dblwordsSwap to indicate it's about double-words

* fixed wrong preprocessor directive unnoticed by clang

* added networking choice option to cmake build, fix to printf warning

- for cmake specify the networking to use with -DMAIKO_NETWORK_TYPE=<type>
- with <type> one of: NONE, SUN_DLPI, SUN_NIT, NETHUB
- e.g.: cmake .. -DMAIKO_NETWORK_TYPE=NETHUB

* integrated improvement to sendPacket() proposed by nbriggs

* integrated fix for SIGBUS on 32-bit big-endian, provided by nbriggs

* MAIKO_ENABLE_ETHERNET should not be unconditionally set on Solaris systems

* Receiving an ethernet packet is an ether interrupt but not an i/o interrupt.

Co-authored-by: dev hawala <devhawala@x.y>
Co-authored-by: Nick Briggs <nicholas.h.briggs@gmail.com>

CMakeLists.txt

@@ -72,10 +72,30 @@ IF(MAIKO_DISPLAY_X11)
   )
 ENDIF()
 
+# according to: https://cmake.org/pipermail/cmake/2016-October/064342.html
+# the following 2 lines should produce a dropdown-box in the cmake-gui
+# but this will happen only after running the command line version of cmake,
+# possibly after "clearing the cache" (i.e. starting with a fresh build directory)
+SET(MAIKO_NETWORK_TYPE NONE CACHE STRING "Type of networking to use: one of: NONE, SUN_DLPI, SUN_NIT, NETHUB")
+SET_PROPERTY(CACHE MAIKO_NETWORK_TYPE PROPERTY STRINGS NONE SUN_DLPI SUN_NIT NETHUB)
+
+# configure networking implementation to use
+IF(MAIKO_NETWORK_TYPE STREQUAL "NETHUB")
+  LIST(APPEND MAIKO_DEFINITIONS "-DMAIKO_ENABLE_NETHUB")
+  MESSAGE("-- Configured for NETHUB network support")
+ELSEIF(MAIKO_NETWORK_TYPE STREQUAL "SUN_DLPI")
+  LIST(APPEND MAIKO_DEFINITIONS "-DMAIKO_ENABLE_ETHERNET -DUSE_DLPI")
+  MESSAGE("-- Configured for (SunOS) DLPI networking")
+ELSEIF(MAIKO_NETWORK_TYPE STREQUAL "SUN_NIT")
+  LIST(APPEND MAIKO_DEFINITIONS "-DMAIKO_ENABLE_ETHERNET -DUSE_NIT")
+  MESSAGE("-- Configured for (SunOS) NIT networking")
+ELSEIF(NOT MAIKO_NETWORK_TYPE STREQUAL "NONE")
+  MESSAGE(WARNING "Invalid option given for MAIKO_NETWORK_TYPE, must be one of:\nNONE, SUN_DLPI, SUN_NIT, NETHUB")
+ENDIF()
+
 IF(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
   LIST(APPEND MAIKO_DEFINITIONS
     "-DOS5"
-    "-DUSE_DLPI"
   )
 ENDIF()
 
@@ -142,7 +162,9 @@ SET(MAIKO_SRCS
     src/dspif.c
     src/dspsubrs.c
     src/eqf.c
-    src/ether.c
+    src/ether_common.c
+    src/ether_sunos.c
+    src/ether_nethub.c
     src/findkey.c
     src/foreign.c
     src/fp.c