get_raw_packet: The read length check is stricter than necessary.

Allow reads with excess data beyond the packet to succeed if the
packet is still well-formed.

src/dhcp.c

@@ -195,7 +195,7 @@ static ssize_t get_raw_packet(struct client_state_t cs[static 1],
         return -1;
     }
     size_t iphdrlen = ntohs(packet.ip.tot_len);
-    if ((size_t)inc != iphdrlen)
+    if ((size_t)inc < iphdrlen)
         return -2;
     if (!cs->using_dhcp_bpf && !get_raw_packet_validate_bpf(&packet))
         return -2;