Maiko code changes needed to compile on Alpine Linux with clang. (#456)

* Changes needed to compile maiko on Alpine Linux with clang.  Switching to Alpine on github actions to streamline maiko release builds

* Changes needed to compile maiko on Alpine Linux with clang.

Switching to Alpine on github actions to streamline maiko release builds.

  * ether_nethub.c missing a couple of includes, and incorrectly including
    <sys/poll.h> instead of plain <poll.h>
  * <dirent.h> does not define MAXNAMLEN on Alpine Linux, but "locfile.h"
    compensates for this already, if it is modified to include <limits.h>,
    so use this in "dirdefs.h".

---------

Co-authored-by: Nick Briggs <nicholas.h.briggs@gmail.com>

src/ether_nethub.c

@@ -14,8 +14,10 @@
 #include <string.h>
 #include <unistd.h>
 #include <sys/socket.h>
+#include <sys/select.h>
+#include <sys/types.h>
 #include <arpa/inet.h>
-#include <sys/poll.h>
+#include <poll.h>
 #include <signal.h>
 #include <fcntl.h>
 #include <errno.h>