package/libpcap: disable dbus to break circular dependency

package/libpcap: disable dbus to break circular dependency

The optional dbus dependency of libpcap creates a circular dependency
chain:

$ make libpcap-show-recursive-depends

Recursion detected for  : systemd
which is a dependency of: dbus
which is a dependency of: libpcap
which is a dependency of: iptables
which is a dependency of: systemd
make: *** [package/libpcap/libpcap.mk:55: libpcap-show-recursive-depends] Error 1

Of all these dependencies the one of libpcap on dbus seems to be less
useful. Drop it.

Fixes:
http://autobuild.buildroot.net/results/0b5d18bff816cbcee11e8645449701722d956de5/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>