BUG: vars: Fix 'set-var' converter because of a typo

BUG: vars: Fix 'set-var' converter because of a typo

The 'set-var' converter uses function smp_conv_store (vars.c). In this function,
we should use the first argument (index 0) to retrieve the variable name and its
scope. But because of a typo, we get the scope of the second argument (index
1). In this case, there is no second argument. So the scope used was always 0
(SCOPE_SESS), always setting the variable in the session scope.

So, due to this bug, this rules

  tcp-request content accept if { src,set-var(txn.foo) -m found }

always set the variable 'sess.foo' instead of 'txn.foo'.