net: Make IP alignment calulations clearer.

The assignmnet:

	ip_align = strict ? 2 : NET_IP_ALIGN;

in compare_pkt_ptr_alignment() trips up Coverity because we can only
get to this code when strict is true, therefore ip_align will always
be 2 regardless of NET_IP_ALIGN's value.

So just assign directly to '2' and explain the situation in the
comment above.

Reported-by: "Gustavo A. R. Silva" <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

kernel/bpf/verifier.c

@@ -808,11 +808,15 @@ static int check_pkt_ptr_alignment(const struct bpf_reg_state *reg,
 		reg_off += reg->aux_off;
 	}
 
-	/* skb->data is NET_IP_ALIGN-ed, but for strict alignment checking
-	 * we force this to 2 which is universally what architectures use
-	 * when they don't set CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.
+	/* For platforms that do not have a Kconfig enabling
+	 * CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS the value of
+	 * NET_IP_ALIGN is universally set to '2'.  And on platforms
+	 * that do set CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, we get
+	 * to this code only in strict mode where we want to emulate
+	 * the NET_IP_ALIGN==2 checking.  Therefore use an
+	 * unconditional IP align value of '2'.
 	 */
-	ip_align = strict ? 2 : NET_IP_ALIGN;
+	ip_align = 2;
 	if ((ip_align + reg_off + off) % size != 0) {
 		verbose("misaligned packet access off %d+%d+%d size %d\n",
 			ip_align, reg_off, off, size);