iwlwifi: refactor packet reception code

This patch fixes a number of issues in iwl_rx_reply_rx and
iwl_pass_packet_to_mac80211.  These issues stem from the complexities of
managing two different types of packet commands for different hardware.

- Unify code handling rx_phy_res in SKB or cached to eliminate redundancy and
remove potential NULL pointer accesses
- Replace magic number with proper constant
- Optimize functions by moving early exit conditions before computation
- Comment code and improve some variable names
- Remove redundant computation in iwl_pass_packet_to_mac80211 by passing in the
correct, already-computed arguments.

Signed-off-by: Daniel C Halperin <daniel.c.halperin@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-commands.h b/drivers/net/wireless/iwlwifi/iwl-commands.h
index 68d7719..9398ad7 100644
--- a/drivers/net/wireless/iwlwifi/iwl-commands.h
+++ b/drivers/net/wireless/iwlwifi/iwl-commands.h
@@ -1156,6 +1156,7 @@
 #define RX_RES_PHY_FLAGS_SHORT_PREAMBLE_MSK	cpu_to_le16(1 << 2)
 #define RX_RES_PHY_FLAGS_NARROW_BAND_MSK	cpu_to_le16(1 << 3)
 #define RX_RES_PHY_FLAGS_ANTENNA_MSK		cpu_to_le16(0xf0)
+#define RX_RES_PHY_FLAGS_ANTENNA_POS		4
 
 #define RX_RES_STATUS_SEC_TYPE_MSK	(0x7 << 8)
 #define RX_RES_STATUS_SEC_TYPE_NONE	(0x0 << 8)