Merge "Adjust RFCOMM low rx watermark" into main

#define BTA_RFC_MTU_SIZE (L2CAP_MTU_SIZE - L2CAP_MIN_OFFSET - RFCOMM_DATA_OVERHEAD)

// The port receive queue low watermark level, in number of buffers.

#define PORT_RX_BUF_LOW_WM 4

#define PORT_RX_BUF_LOW_WM 8

// The port receive queue high watermark level, in number of buffers.

#define PORT_RX_BUF_HIGH_WM 10