modem: ubx: Change request buffer to be void

So this API can be used to send frames with a different encoding than
UBX. This enables UBX drivers to send RTCM3 correction frames using UBX
API, without having to switch over modem pipes.

Signed-off-by: Luis Ubieda <luisf@croxel.com>

Author: ubieda

include/zephyr/modem/ubx.h

@@ -53,7 +53,7 @@ struct modem_ubx_match {
 
 struct modem_ubx_script {
 	struct {
-		const struct ubx_frame *buf;
+		const void *buf;
 		uint16_t len;
 	} request;
 	struct {