serial_port_linux: Add missing include sys/time.h

POSIX says `struct timeval` is defined if <sys/time.h> is included.

Adding this header allow to build against musl-libc.

Signed-off-by: Romain Naour <romain.naour@smile.fr>

hal/serial/linux/serial_port_linux.c

@@ -29,6 +29,7 @@
 #include <termios.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <sys/time.h>
 
 #include "hal_serial.h"
 #include "hal_time.h"