nmap: fix build on MacOS X

The configure script (for libdnet) seems to find <net/bpf.h>
and detect some BSD stuff.

The lidnet's Makefile wants to include eth-bsd.c, arp-bsd.c
and other BSD friends.

This seems to put a cork on it, and no BSD stuff appears anymore.
[at least on my system].

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

net/nmap/Makefile

@@ -90,7 +90,9 @@ CONFIGURE_ARGS += \
 	--without-liblua \
 	--without-zenmap
 
-CONFIGURE_VARS += CXXFLAGS="$$$$CXXFLAGS -fno-builtin"
+CONFIGURE_VARS += \
+	ac_cv_dnet_bsd_bpf=no \
+	CXXFLAGS="$$$$CXXFLAGS -fno-builtin"
 
 ifeq ($(BUILD_VARIANT),ssl)
 	CONFIGURE_ARGS += --with-openssl="$(STAGING_DIR)/usr"