nameserv: adopt some include directives from sysincl.h

Move headers specific to name resolving to nameserv.c. This should hide
the system MIN/MAX macros from the rest of the code.

nameserv.c

@@ -30,6 +30,9 @@
 
 #include "sysincl.h"
 
+#include <netdb.h>
+#include <resolv.h>
+
 #include "nameserv.h"
 #include "util.h"
 

sysincl.h

@@ -38,10 +38,8 @@
 #include <grp.h>
 #include <inttypes.h>
 #include <math.h>
-#include <netdb.h>
 #include <netinet/in.h>
 #include <pwd.h>
-#include <resolv.h>
 #include <signal.h>
 #include <stdarg.h>
 #include <stddef.h>