iwl-3945: add #ifdef CONFIG_IWL3945_LEDS to avoid compile warning.

When building the wireless-next-2.6 tree with CONFIG_IWL3945 (for building
iwl-3945 driver) and where CONFIG_IWL3945_LEDS is not set,
we get this warning:
drivers/net/wireless/iwlwifi/iwl-3945.c: In function
'iwl3945_pass_packet_to_mac80211':
drivers/net/wireless/iwlwifi/iwl-3945.c:633: warning: unused variable 'hdr'

This patch adds #ifdef to iwl3945_pass_packet_to_mac80211() to avoid this
warning. (The variable 'hdr' is used only if CONFIG_IWL3945_LEDS is set)

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>