iptables segfault on HTC One SV

The "hostname" argument to getaddrinfo() is allowed to be NULL:

```
int
getaddrinfo(const char *hostname, const char *servname,
    const struct addrinfo *hints, struct addrinfo **res)
{
	struct addrinfo sentinel;
	struct addrinfo *cur;
	int error = 0;
	struct addrinfo ai;
	struct addrinfo ai0;
	struct addrinfo *pai;
	const struct explore *ex;

	/* hostname is allowed to be NULL */
	/* servname is allowed to be NULL */
	/* hints is allowed to be NULL */
	assert(res != NULL);

	memset(&sentinel, 0, sizeof(sentinel));
```

Stock iptables passes in a NULL hostname when it just wants to look up a port (service) number:

```
/**
 * @name:	port name, or number as a string (e.g. "http" or "80")
 *
 * Resolve a port name to a number. Returns the port number in integral
 * form on success, or <0 on error. (errno will not be set.)
 */
static int xtables_getportbyname(const char *name)
{
	struct addrinfo *res = NULL, *p;
	int ret;

	ret = getaddrinfo(NULL, name, NULL, &res);
```

However, the fork of Bionic on the HTC One SV ROM, JB 4.1.2, erroneously calls strlen() on this argument without ensuring that it isn't NULL:

```
00033640 <getaddrinfo>:
   33640:       e92d 4ff0       stmdb   sp!, {r4, r5, r6, r7, r8, r9, sl, fp, lr}
   33644:       b0e9            sub     sp, #420
   33646:       4617            mov     r7, r2          ; r7 = hints
   33648:       4688            mov     r8, r1          ; r8 = servname
   3364a:       9309            str     r3, [sp, #36]   ; sp+36 = res
   3364c:       4605            mov     r5, r0          ; r5 = hostname
   3364e:       f8df 3864       ldr.w   r3, [pc, #2148]
   33652:       9909            ldr     r1, [sp, #36]
   33654:       447b            add     r3, pc
   33656:       681b            ldr     r3, [r3, #0]
   33658:       930c            str     r3, [sp, #48]
   3365a:       681a            ldr     r2, [r3, #0]
   3365c:       9267            str     r2, [sp, #412]
   3365e:       b931            cbnz    r1, 3366e       ; taken if res != NULL (true in this case)

[snip]

   3366e:       f7e3 ee8c       blx     17388 <strlen>  ; strlen(hostname)
```

This causes a segfault when AFWall tries to add a rule involving a port number, e.g.

```
iptables -A OUTPUT -p udp --dport 53 -j RETURN
```

We can work around this by passing in a dummy hostname from our builtin iptables binary.  (The system iptables binary will still crash, so it can't be used on a device with this bug.)

Note that this pull request includes a couple of other fixes too, for Travis builds and for the Bug #212.