iwlwifi: refactor tx byte count table usage

This patch drops unreadable usage of IWL_SET/GET_BITS16 in byte count
tables handling
This patch also cleans a bit the byte count table code and adds
WARN_ON traps on invalid values

This patch is pure cleanup, no functional changes.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-fh.h

@@ -393,4 +393,9 @@
 /* TCSR: tx_config register values */
 #define FH_RSCSR_FRAME_SIZE_MSK	(0x00003FFF)	/* bits 0-13 */
 
+#define TFD_QUEUE_SIZE_MAX      (256)
+#define TFD_QUEUE_SIZE_BC_DUP	(64)
+#define TFD_QUEUE_BC_SIZE	(TFD_QUEUE_SIZE_MAX + TFD_QUEUE_SIZE_BC_DUP)
+
+
 #endif /* !__iwl_fh_h__ */