package/openpowerlink: use pcap-config to fix static linking with libpcap

package/openpowerlink: use pcap-config to fix static linking with libpcap

When linking demo_mn_console statically with pcap, the CMake build
system forget to link with other libraries linked with libpcap
(-lnl-genl-3 -lnl-3 -ldbus-1 -pthread).

[100%] Linking C executable demo_mn_console
lib64/libpcap.a(pcap-linux.o): In function nl80211_init': pcap-linux.c:(.text+0x41e): undefined reference tonl_socket_alloc'

To fix this, the build system could use pcap-config:
pcap-config --libs --static
-L/path/to/sysroot/usr/lib -lpcap -L/path/to/sysroot/usr/lib/.libs
-lnl-genl-3 -lnl-3 -L/path/to/sysroot/usr/lib -ldbus-1 -pthread

Also don't use getopt() from contrib directory to avoid a clash with
libc definition.

Fixes:
http://autobuild.buildroot.net/results/f43/f437d09ac6c689c911e1885b95da33b692f2cb3c
http://autobuild.buildroot.net/results/385/3859dc0f4de7e3284a96d5841f040f69f71842df
https://github.com/OpenAutomationTechnologies/openPOWERLINK_V2/issues/187

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Tested-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>