unix: move net/if.h include

This commit moves the net/if.h include into src/getaddrinfo.c to
prevent AIX compilation errors. With these symbols exposed
publicly, Node.js compilation failed on AIX by exposing Free(),
which conflicts with another API.

Refs: https://github.com/nodejs/node/pull/16835
Refs: https://github.com/libuv/libuv/pull/1445
PR-URL: https://github.com/libuv/libuv/pull/1622
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

include/uv-unix.h

@@ -32,7 +32,6 @@
 #include <netinet/tcp.h>
 #include <arpa/inet.h>
 #include <netdb.h>
-#include <net/if.h>
 
 #include <termios.h>
 #include <pwd.h>

src/unix/getaddrinfo.c

@@ -32,6 +32,7 @@
 #include <stddef.h> /* NULL */
 #include <stdlib.h>
 #include <string.h>
+#include <net/if.h> /* if_indextoname() */
 
 /* EAI_* constants. */
 #include <netdb.h>