libertas: rework event subscription

This patch moves re-works the implementation of event subscription
via debugfs. For this:

* it tells cmd.c and cmdresp.c about CMD_802_11_SUBSCRIBE_EVENT
* removes lots of low-level cmd stuff from debugfs.c
* create unified functions to read/write snr, rssi, bcnmiss and
  failcount
* introduces #define's for subscription event bitmask values
* add a function to search for a specific element in an IE
  (a.k.a. TLV)
* add a function to find out the size of the TLV. This is needed
  because lbs_prepare_and_send_command() has an argument for a
  data buffer, but not for it's lengths and TLVs can be, by
  definition, vary in size.
* fix a bug where it was not possible to disable an event

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/libertas/hostcmd.h b/drivers/net/wireless/libertas/hostcmd.h
index f4a265d..614db6c 100644
--- a/drivers/net/wireless/libertas/hostcmd.h
+++ b/drivers/net/wireless/libertas/hostcmd.h
@@ -151,6 +151,13 @@
 struct cmd_ds_802_11_subscribe_event {
 	__le16 action;
 	__le16 events;
+
+	/* A TLV to the CMD_802_11_SUBSCRIBE_EVENT command can contain a
+	 * number of TLVs. From the v5.1 manual, those TLVs would add up to
+	 * 40 bytes. However, future firmware might add additional TLVs, so I
+	 * bump this up a bit.
+	 */
+	u8 tlv[128];
 };
 
 /*