nimble/host: Fix unreachable code if BLE_L2CAP_JOIN_RX_FRAGS is enabled
nimble/host: Fix unreachable code if BLE_L2CAP_JOIN_RX_FRAGS is enabled

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble