drivers: modem: cellular: hl7800 fix enter cmux

The OK response should be processed before entering CMUX mode.

Use UART ISR mode by default.

Fix warnings and errors produced by the sample.

Signed-off-by: Ryan Erickson <ryan.erickson@ezurio.com>
(cherry picked from commit bbcf23e)

Author: rerickson1

drivers/modem/modem_cellular.c

@@ -1924,7 +1924,7 @@ MODEM_CHAT_SCRIPT_CMDS_DEFINE(swir_hl7800_init_chat_script_cmds,
 			      MODEM_CHAT_SCRIPT_CMD_RESP("", ok_match),
 			      MODEM_CHAT_SCRIPT_CMD_RESP("AT+CIMI", cimi_match),
 			      MODEM_CHAT_SCRIPT_CMD_RESP("", ok_match),
-			      MODEM_CHAT_SCRIPT_CMD_RESP_NONE("AT+CMUX=0,0,5,127", 0));
+			      MODEM_CHAT_SCRIPT_CMD_RESP("AT+CMUX=0,0,5,127", ok_match));
 
 MODEM_CHAT_SCRIPT_DEFINE(swir_hl7800_init_chat_script, swir_hl7800_init_chat_script_cmds,
 			 abort_matches, modem_cellular_chat_callback_handler, 10);

samples/net/cellular_modem/boards/mg100.conf

@@ -1,2 +1,3 @@
 CONFIG_MODEM_HL7800=n
-CONFIG_UART_ASYNC_API=y
+CONFIG_MODEM_CELLULAR_CMUX_MAX_FRAME_SIZE=255
+CONFIG_NET_BUF_TX_COUNT=32

samples/net/cellular_modem/boards/pinnacle_100_dvk.conf

@@ -1,2 +1,3 @@
 CONFIG_MODEM_HL7800=n
-CONFIG_UART_ASYNC_API=y
+CONFIG_MODEM_CELLULAR_CMUX_MAX_FRAME_SIZE=255
+CONFIG_NET_BUF_TX_COUNT=32