leaking_addresses: explicitly name variable used in regex

Currently sub routine may_leak_address() is checking regex against Perl
special variable $_ which is _fortunately_ being set correctly in a loop
before this sub routine is called.  We already have declared a variable
to hold this value '$line' we should use it.

Use $line in regex match instead of implicit $_

Signed-off-by: Tobin C. Harding <me@tobin.cc>