NetworkPkg: Fix unable to build OVMF with -D NETWORK_ENABLE=0

https://bugzilla.tianocore.org/show_bug.cgi?id=4829

7f17a15 (2024/02/22)
"OvmfPkg: Shell*.inc: allow building without network support"
breaks building OVMF with `-D NETWORK_ENABLE=0`.

Before this commit we could build OVMF e.g. with the following
command in the OvmfPkg directory:

./build.sh -D NETWORK_ENABLE=0

After the commit the same command fails early with:

/home/user/OpenSource/edk2/OvmfPkg/OvmfPkgX64.dsc(15):
error F001: Pcd (gEfiNetworkPkgTokenSpaceGuid.PcdAllowHttpConnections)
defined in DSC is not declared in DEC files referenced in INF files in
FDF. Arch: ['X64']

This commit conditionally removes the undefined Pcd reference in
NetworkPkg which is part of this issue.

Similar changes are needed in separate commits for
OvmfPkg (and for ArmVirtPkg, since the issue also
exists there, although masked by another issue).

Signed-off-by: Mike Beaton <mjsbeaton@gmail.com>

NetworkPkg/NetworkPcds.dsc.inc

@@ -11,6 +11,6 @@
 #
 ##
 
-!if $(NETWORK_ALLOW_HTTP_CONNECTIONS) == TRUE
+!if ($(NETWORK_ENABLE) == TRUE) AND ($(NETWORK_ALLOW_HTTP_CONNECTIONS) == TRUE)
   gEfiNetworkPkgTokenSpaceGuid.PcdAllowHttpConnections|TRUE
 !endif