openthread: Increase size of app parititon in ot_br example
# Note: if you have increased the bootloader size, make sure to update the offsets to avoid overlap
nvs, data, nvs, 0x9000, 0x6000,
phy_init, data, phy, 0xf000, 0x1000,
-factory, app, factory, 0x10000, 1400K,
+factory, app, factory, 0x10000, 1500K,
ot_storage, data, 0x3a, , 0x2000,
