sln: Fix set-but-unused gcc47 warning
ral: Fix set-but-unused gcc47 warning
iwn: Fix set-but-unused gcc47 warning
ath: Partly fix set-but-unused gcc47 warning
acpica: Fix set-but-unused gcc47 warning
wlan: Partly fix set-but-unused gcc47 warning
ip6/mroute: Partly fix set-but-unused gcc47 warning
pf: Fix set-but-unused gcc47 warning