Merge #996 branch 'eugeneia/public-packet_t' into next

Grabbing revert of the packet_t type since we decided to go with
'struct packet' directly instead.

See discussion at #997 (comment)

src/README.md

@@ -333,7 +333,7 @@ Returns a structure holding ring statistics for the *link*:
 
 ## Packet (core.packet)
 
-A *packet* is an FFI object of type `packet.packet_t` representing a network
+A *packet* is an FFI object of type `struct packet` representing a network
 packet that is currently being processed. The packet is used to explicitly
 manage the life cycle of the packet. Packets are explicitly allocated and freed
 by using `packet.allocate` and `packet.free`. When a packet is received using
@@ -345,7 +345,7 @@ freed. The number of allocatable packets is limited by the size of the
 underlying “freelist”, e.g. a pool of unused packet objects from and to which
 packets are allocated and freed.
 
-— Ctype **packet.packet_t**
+— Type **struct packet**
 
 ```
 struct packet {

src/core/packet.lua

@@ -13,8 +13,8 @@ local counter  = require("core.counter")
 
 require("core.packet_h")
 
-packet_t = ffi.typeof("struct packet")
-local packet_ptr_t = ffi.typeof("$ *", packet_t)
+local packet_t = ffi.typeof("struct packet")
+local packet_ptr_t = ffi.typeof("struct packet *")
 local packet_size = ffi.sizeof(packet_t)
 local header_size = 8
 max_payload = tonumber(C.PACKET_PAYLOAD_SIZE)