package/netsniff-ng: fix static build of mausezahn

The configure script fails to detect libpcap in static build because it
does not take into account the libnl dependency on link. As a result the
configure script silently disables mausezahn build even when
BR2_PACKAGE_NETSNIFF_NG_MAUSEZAHN is enabled. Add upstream patch to use
pkg-config for libpcap link flags.

Cc: Joris Lijssens <joris.lijssens@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>