Prevent mesh_fwding field in network config when CONFIG_MESH is disabled

Prevent mesh_fwding field in network config when CONFIG_MESH is disabled

mesh_fwding and no_auto_peer configuration items are parsed within ifdef
CONFIG_MESH, but they are written without matching conditional
compilation. This could result in configuration files that cannot be
read back by the same wpa_supplicant binary if either of those
configuration values could end up getting modified.

Make the configuration file writing code use matching ifdef CONFIG_MESH
for these parameters to be consistent with the configuration reader.

Signed-off-by: sunilravi <sunilravi@google.com>