Disable libnl by default when building with included libpcap

Libpcap only needs libnl for monitor-mode sniffing. Disabling it lets us
not worry about which -lnl or -lnl-3 linker argument to include in our
own LIBS, so Nmap builds properly no matter whether libnl is present or
not.

libpcap/NMAP_MODIFICATIONS/0003-Disable-unnecessary-features.patch

@@ -1,7 +1,29 @@
+The following features are disabled:
+
+* monitor-mode sniffing of wireless interfaces on Linux, via libnl
+* building shared libraries
+* Bluetooth support
+* canusb support
+* CAN support
+* dbus capture support
+
 diff --git a/libpcap/configure.in b/libpcap/configure.in
 index 5386062..8ceddd7 100644
 --- a/libpcap/configure.in
 +++ b/libpcap/configure.in
+@@ -441,10 +441,10 @@ linux)
+ 	# Do we have libnl?
+ 	#
+ 	AC_ARG_WITH(libnl,
+-	AC_HELP_STRING([--without-libnl],[disable libnl support @<:@default=yes, on Linux, if present@:>@]),
++	AC_HELP_STRING([--without-libnl],[disable libnl support @<:@default=disabled@:>@]),
+ 		with_libnl=$withval,,)
+ 
+-	if test x$with_libnl != xno ; then
++	if test x$with_libnl = xyes ; then
+ 		have_any_nl="no"
+ 
+ 		#
 @@ -1285,8 +1285,8 @@ solaris*)
  esac
  

libpcap/configure

@@ -1388,8 +1388,7 @@ Optional Packages:
   --without-gcc           don't use gcc
   --with-sita             include SITA support
   --with-pcap=TYPE        use packet capture TYPE
-  --without-libnl         disable libnl support [default=yes, on Linux, if
-                          present]
+  --without-libnl         disable libnl support [default=disabled]
   --with-dag[=DIR]        include Endace DAG support ["yes", "no" or DIR;
                           default="yes" on BSD and Linux if present]
   --with-dag-includes=DIR Endace DAG include directory
@@ -5500,7 +5499,7 @@ if test "${with_libnl+set}" = set; then :
 fi
 
 
-	if test x$with_libnl != xno ; then
+	if test x$with_libnl = xyes ; then
 		have_any_nl="no"
 
 		#

libpcap/configure.in

@@ -441,10 +441,10 @@ linux)
 	# Do we have libnl?
 	#
 	AC_ARG_WITH(libnl,
-	AC_HELP_STRING([--without-libnl],[disable libnl support @<:@default=yes, on Linux, if present@:>@]),
+	AC_HELP_STRING([--without-libnl],[disable libnl support @<:@default=disabled@:>@]),
 		with_libnl=$withval,,)
 
-	if test x$with_libnl != xno ; then
+	if test x$with_libnl = xyes ; then
 		have_any_nl="no"
 
 		#