nwfilter: Increase buffer size for libpcap

Libpcap 1.5 requires a larger buffer than previous pcap versions.
Adjust the size of the buffer to 128kb.

This patch should address symptoms in BZ 1071181 and BZ 731059
Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>

src/nwfilter/nwfilter_dhcpsnoop.c

@@ -250,7 +250,11 @@ struct _virNWFilterDHCPDecodeJob {
 # define DHCP_PKT_BURST         50 /* pkts/sec */
 # define DHCP_BURST_INTERVAL_S  10 /* sec */
 
-# define PCAP_BUFFERSIZE        (DHCP_PKT_BURST * PCAP_PBUFSIZE / 2)
+/*
+ * libpcap 1.5 requires a 128kb buffer
+ * 128 kb is bigger than (DHCP_PKT_BURST * PCAP_PBUFSIZE / 2)
+ */
+# define PCAP_BUFFERSIZE        (128 * 1024)
 
 # define MAX_QUEUED_JOBS        (DHCP_PKT_BURST + 2 * DHCP_PKT_RATE)