staging: r8712u: fix bug in r8712_recv_indicatepkt()

64bit arches have a buggy r8712u driver, let's fix it.

skb->tail must be set properly or network stack behavior is undefined.

Addresses https://bugzilla.redhat.com/show_bug.cgi?id=847525
Addresses https://bugzilla.kernel.org/show_bug.cgi?id=45071

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Dave Jones <davej@redhat.com>
Cc: stable <stable@vger.kernel.org> [2.6.37+]
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>