Changed my mind about having CONFIG_UML_NET_PCAP enabled by default

in defconfig.  This would cause the default config to break on
any system without libpcap, so disabling it by default is better.

arch/um/defconfig

@@ -86,7 +86,7 @@ CONFIG_UML_NET_TUNTAP=y
 CONFIG_UML_NET_SLIP=y
 CONFIG_UML_NET_DAEMON=y
 CONFIG_UML_NET_MCAST=y
-CONFIG_UML_NET_PCAP=y
+# CONFIG_UML_NET_PCAP is not set
 CONFIG_DUMMY=y
 # CONFIG_BONDING is not set
 # CONFIG_EQUALIZER is not set