Adjust libnetwork.so to no longer depend on libbe.so.

* Libbe is not available when cross-building the *_bootstrap packages,
  so no libnetwork could not be used either, which made building 
  anything network-related impossible.
* The only code in libnetwork that requires libbe is the notification,
  so I moved that over to libbnetapi. Non-C++ applications can't use
  the notification calls anyway, as their interface is C++-only.

src/kits/network/Jamfile

@@ -1,6 +1,6 @@
 SubDir HAIKU_TOP src kits network ;
 
-UsePrivateHeaders app libroot net shared ;
+UsePrivateHeaders libroot net shared ;
 
 local services = [ FGristFiles services ] ;
 SEARCH on $(services) = [ FDirName $(SUBDIR) libbind defaults ] ;
@@ -16,11 +16,9 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 		SharedLibrary $(libnetwork) :
 			init.cpp
 			interfaces.cpp
-			notifications.cpp
 			socket.cpp
 			r5_compatibility.cpp
 			:
-			be
 			<libbind!$(architecture)>libbind.o
 			$(TARGET_LIBSUPC++)
 			;

src/kits/network/libnetapi/Jamfile

@@ -1,6 +1,6 @@
 SubDir HAIKU_TOP src kits network libnetapi ;
 
-UsePrivateHeaders net shared ;
+UsePrivateHeaders app net shared ;
 
 UseHeaders [ FDirName $(HAIKU_TOP) src libs compat freebsd_network compat ]
 	: true ;
@@ -17,6 +17,8 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 		Includes [ FGristFiles $(HPKG_SOURCES) ]
 			: [ BuildFeatureAttribute zlib : headers ] ;
 
+		UsePrivateSystemHeaders ;
+
 		if [ FIsBuildFeatureEnabled openssl ] {
 			SubDirC++Flags -DOPENSSL_ENABLED ;
 			UseBuildFeatureHeaders openssl ;
@@ -73,6 +75,8 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 			# TODO: another add-on for file:// (a much simpler one)
 			FileRequest.cpp
 
+			notifications.cpp
+
 			$(md5Sources)
 
 			Url.cpp