packets: Remove unnecessary "packed" annotations.

I know of two reasons to mark a structure as "packed".  The first is
because the structure must match some defined interface and therefore
compiler-inserted padding between or after members would cause its layout
to diverge from that interface.  This is not a problem in a structure that
follows the general alignment rules that are seen in ABIs for all the
architectures that OVS cares about: basically, that a struct member needs
to be aligned on a boundary that is a multiple of the member's size.

The second reason is because instances of the struct tend to be at
misaligned addresses.

struct eth_header and struct vlan_eth_header are normally aligned on
16-bit boundaries (at least), and they contain only 16-bit members, so
there's no need to pack them.  This commit removes the packed annotation.

This commit also removes the packed annotation from struct llc_header.
Since that struct only contains 8-bit members, I don't know of any benefit
to packing it, period.

This commit also removes a few more packed annotations that are much less
important.

When these packed annotations were removed, it caused a few warnings
related to casts from 'uint8_t *' to more strictly aligned pointer types,
related to struct ovs_action_push_tnl.  That's because that struct had a
trailing member used to store packet headers, that was declared as
a uint8_t[].  Before, when this was cast to 'struct eth_header *', there
was no change in alignment since eth_header was packed; now that
eth_header is not packed, the compiler considers it suspicious.  This
commit avoids that problem by changing the member from uint8_t[] to
uint32_t[], which assures the compiler that it is properly aligned.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Joe Stringer <joe@ovn.org>

lib/odp-util.c

@@ -1136,7 +1136,7 @@ ovs_parse_tnl_push(const char *s, struct ovs_action_push_tnl *data)
         return -EINVAL;
     }
     eth = (struct eth_header *) data->header;
-    l3 = (data->header + sizeof *eth);
+    l3 = (struct ip_header *) (eth + 1);
     ip = (struct ip_header *) l3;
     ip6 = (struct ovs_16aligned_ip6_hdr *) l3;
     if (!ovs_scan_len(s, &n, "header(size=%"SCNi32",type=%"SCNi32","