The following Python script was tested with Shape files, PostGIS layers, and SpatiaLite using QGIS 2.8.2 on Windows 7. Specify the field you want to filter in the first code line (replace rtt).

# specify field to filter
field_name = 'rtt'

# get active layer
layer = iface.activeLayer()

# get reference to the field named above
fni = layer.fieldNameIndex(field_name)
f = layer.dataProvider().fields()

# get field type, necessary to build valid SQL string
is_string = False
if f[fni].type() in [7, 10]:
    is_string = True

# get list of unique values
unique_values = layer.uniqueValues(fni)
for i in unique_values:
    # add layer to the map
    lyr_copy = iface.addVectorLayer(layer.source(), layer.name() + '_' + str(i), layer.providerType())
    # build subset string in SQL like syntax
    if is_string:
        lyr_copy.setSubsetString('"%s" = \'%s\'' % (field_name, i))
    else:
        lyr_copy.setSubsetString('"%s" = %d' % (field_name, int(i)))

ESRI file Geodatabase didn't work since for all field indices layer.uniqueValues(fni) returns the list unique values of the first attribute. Maybe an issue of QGIS 2.8.2.

The following Python script was tested with Shape files, PostGIS layers, and SpatiaLite using QGIS 2.8.2 on Windows 7. Specify the field you want to filter in the first code line (replace rtt).

# specify field to filter
field_name = 'rtt'

# get active layer
layer = iface.activeLayer()

# get reference to the field named above
fni = layer.fieldNameIndex(field_name)
f = layer.dataProvider().fields()

# get field type, necessary to build valid SQL string
is_string = False
if f[fni].type() in [7, 10]:
    is_string = True

# get list of unique values
unique_values = layer.uniqueValues(fni)
for i in unique_values:
    # add layer to the map
    lyr_copy = iface.addVectorLayer(layer.source(), layer.name() + '_' + str(i), layer.providerType())
    # build subset string in SQL like syntax
    if is_string:
        lyr_copy.setSubsetString('"%s" = \'%s\'' % (field_name, i))
    else:
        lyr_copy.setSubsetString('"%s" = %d' % (field_name, int(i)))

ESRI file Geodatabase didn't work for me since for all field indices layer.uniqueValues(fni) returns the list of unique values of the first attribute. Thus filtering of an attribut by these values returns an empty list or the wrong result set. Maybe an issue of QGIS 2.8.2.