kismet: Fix static build

Use pcap-config to list optional libpcap dependencies needed for static
link. Otherwise we will see errors like this one:

/br/output/host/usr/mipsel-buildroot-linux-uclibc/sysroot/usr/lib/libpcap.a(pcap-canusb-linux.o):
In function `canusb_close':
pcap-canusb-linux.c:(.text+0xec): undefined reference to `libusb_close'

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
[yann.morin.1998@free.fr: remove the ncurses bits (done differently in
 another patch), fix BR2_PREFER_STATIC_LIB -> BR2_STATIC_LIBS]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>