headers_check: fix perl warnings

According to PBP; best way practice is to use local reference for file
handle and three argument open. Also perl prototypes are a mistake.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: WANG Cong <amwang@redhat.com>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>