Enable CONFIG_DUMMY

Some applications check for network availability by looking for a network device
configured for Internet access.  When TSI is used, there is no such device
available by default, although Internet is accessible.  Then those applications
behave like when the connection is not available.  See
containers/libkrun#576.

Let's enable CONFIG_DUMMY to create a dummy network interface.  Enabling the
option means `dummy0' interface is created automatically in all VMs.  It is
down, i.e. unused, initially.  libkrun can set it up if TSI is used, to make the
applications happy while the device is still bypassed in favour of TSI.  Proper
handling of the device is libkrun's job, this commit just makes it available and
present.

Signed-off-by: Milan Zamazal <mzamazal@redhat.com>

Author: mz-pdm

config-libkrunfw-sev_x86_64

@@ -1305,7 +1305,7 @@ CONFIG_DM_AUDIT=y
 CONFIG_NETDEVICES=y
 CONFIG_NET_CORE=y
 # CONFIG_BONDING is not set
-# CONFIG_DUMMY is not set
+CONFIG_DUMMY=y
 # CONFIG_WIREGUARD is not set
 # CONFIG_EQUALIZER is not set
 # CONFIG_NET_TEAM is not set

config-libkrunfw-tdx_x86_64

@@ -1358,7 +1358,7 @@ CONFIG_DM_AUDIT=y
 CONFIG_NETDEVICES=y
 CONFIG_NET_CORE=y
 # CONFIG_BONDING is not set
-# CONFIG_DUMMY is not set
+CONFIG_DUMMY=y
 # CONFIG_WIREGUARD is not set
 # CONFIG_EQUALIZER is not set
 # CONFIG_NET_TEAM is not set

config-libkrunfw_aarch64

@@ -1386,7 +1386,7 @@ CONFIG_SCSI_SRP_ATTRS=y
 CONFIG_NETDEVICES=y
 CONFIG_NET_CORE=y
 # CONFIG_BONDING is not set
-# CONFIG_DUMMY is not set
+CONFIG_DUMMY=y
 # CONFIG_WIREGUARD is not set
 # CONFIG_EQUALIZER is not set
 # CONFIG_NET_TEAM is not set

config-libkrunfw_riscv64

@@ -1251,7 +1251,7 @@ CONFIG_SCSI_SRP_ATTRS=y
 CONFIG_NETDEVICES=y
 CONFIG_NET_CORE=y
 # CONFIG_BONDING is not set
-# CONFIG_DUMMY is not set
+CONFIG_DUMMY=y
 # CONFIG_WIREGUARD is not set
 # CONFIG_EQUALIZER is not set
 # CONFIG_NET_TEAM is not set

config-libkrunfw_x86_64

@@ -1121,7 +1121,7 @@ CONFIG_DM_AUDIT=y
 CONFIG_NETDEVICES=y
 CONFIG_NET_CORE=y
 # CONFIG_BONDING is not set
-# CONFIG_DUMMY is not set
+CONFIG_DUMMY=y
 # CONFIG_WIREGUARD is not set
 # CONFIG_EQUALIZER is not set
 # CONFIG_NET_TEAM is not set