mac80211: make alignment warning optional

Driver authors should be aware of the alignment requirements, but
not everybody cares about the warning. This patch makes it depend
on a new Kconfig symbol MAC80211_DEBUG_PACKET_ALIGNMENT which can
be enabled regardless of MAC80211_DEBUG and is recommended for
driver authors (only). This also restricts the warning to data
packets so other packets need not be realigned to not trigger the
warning.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/Kconfig b/net/mac80211/Kconfig
index 09c2550..e77592d 100644
--- a/net/mac80211/Kconfig
+++ b/net/mac80211/Kconfig
@@ -98,6 +98,18 @@
 
 	  Say N unless you know you need this.
 
+config MAC80211_DEBUG_PACKET_ALIGNMENT
+	bool "Enable packet alignment debugging"
+	depends on MAC80211
+	help
+	  This option is recommended for driver authors and strongly
+	  discouraged for everybody else, it will trigger a warning
+	  when a driver hands mac80211 a buffer that is aligned in
+	  a way that will cause problems with the IP stack on some
+	  architectures.
+
+	  Say N unless you're writing a mac80211 based driver.
+
 config MAC80211_DEBUG
 	bool "Enable debugging output"
 	depends on MAC80211