ANDROID: xt_qtaguid: Remove unnecessary null checks to ifa_label

'ifa_label' will never be NULL since it isn't a plain pointer but an
array of char values.

../net/netfilter/xt_qtaguid.c:971:11: warning: address of array
'ifa->ifa_label' will always evaluate to 'true'
[-Wpointer-bool-conversion]
                        ifa->ifa_label ? ifa->ifa_label : "(null)");
                        ~~~~~^~~~~~~~~ ~
../net/netfilter/xt_qtaguid.c:972:13: warning: address of array
'ifa->ifa_label' will always evaluate to 'true'
[-Wpointer-bool-conversion]
                if (ifa->ifa_label && !strcmp(ifname, ifa->ifa_label))
                    ~~~~~^~~~~~~~~ ~~

Change-Id: I3c87a5d4b830aaa21a59e9c39cfe0a1d60d7f830
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>