increase the UART buffer sizes to 256

The most critical one is the GPS serial port receive buffer size,
which needs to be at least 128 to support the UBLOX protocol, but it
seems a good idea for people running a FMU without a IO board to
increase the UART buffer sizes generally

nuttx/configs/px4fmu/nsh/defconfig

@@ -245,18 +245,18 @@ CONFIG_USART6_SERIAL_CONSOLE=n
 
 #Mavlink messages can be bigger than 128
 CONFIG_USART1_TXBUFSIZE=512
-CONFIG_USART2_TXBUFSIZE=128
-CONFIG_USART3_TXBUFSIZE=128
-CONFIG_UART4_TXBUFSIZE=128
-CONFIG_UART5_TXBUFSIZE=64
+CONFIG_USART2_TXBUFSIZE=256
+CONFIG_USART3_TXBUFSIZE=256
+CONFIG_UART4_TXBUFSIZE=256
+CONFIG_UART5_TXBUFSIZE=256
 CONFIG_USART6_TXBUFSIZE=128
 
 CONFIG_USART1_RXBUFSIZE=512
-CONFIG_USART2_RXBUFSIZE=128
-CONFIG_USART3_RXBUFSIZE=128
-CONFIG_UART4_RXBUFSIZE=128
-CONFIG_UART5_RXBUFSIZE=128
-CONFIG_USART6_RXBUFSIZE=128
+CONFIG_USART2_RXBUFSIZE=256
+CONFIG_USART3_RXBUFSIZE=256
+CONFIG_UART4_RXBUFSIZE=256
+CONFIG_UART5_RXBUFSIZE=256
+CONFIG_USART6_RXBUFSIZE=256
 
 CONFIG_USART1_BAUD=57600
 CONFIG_USART2_BAUD=115200