doxygen: enable AUTOBRIEF, drop \brief

Especially for short descriptions, it is annoying to have to type \brief for
every single API doc.

Drop all \brief and enable the AUTOBRIEF feature of doxygen, which always takes
the first sentence of an API doc as the brief description.

Change-Id: I11a8a821b065a128108641a2a63fb5a2b1916e87
diff --git a/src/serial.c b/src/serial.c
index 51a32bb..b8c347b 100644
--- a/src/serial.c
+++ b/src/serial.c
@@ -24,7 +24,7 @@
 
 /*! \addtogroup serial
  *  @{
- *  \brief Osmocom serial port helpers
+ *  Osmocom serial port helpers
  */
 
 /*! \file serial.c */
@@ -50,7 +50,7 @@
 # define dbg_perror(x) do { } while (0)
 #endif
 
-/*! \brief Open serial device and does base init
+/*! Open serial device and does base init
  *  \param[in] dev Path to the device node to open
  *  \param[in] baudrate Baudrate constant (speed_t: B9600, B...)
  *  \returns >=0 file descriptor in case of success or negative errno.
@@ -149,7 +149,7 @@
 	return 0;
 }
 
-/*! \brief Change current baudrate
+/*! Change current baudrate
  *  \param[in] fd File descriptor of the open device
  *  \param[in] baudrate Baudrate constant (speed_t: B9600, B...)
  *  \returns 0 for success or negative errno.
@@ -161,7 +161,7 @@
 	return _osmo_serial_set_baudrate(fd, baudrate);
 }
 
-/*! \brief Change current baudrate to a custom one using OS specific method
+/*! Change current baudrate to a custom one using OS specific method
  *  \param[in] fd File descriptor of the open device
  *  \param[in] baudrate Baudrate as integer
  *  \returns 0 for success or negative errno.
@@ -210,7 +210,7 @@
 #endif
 }
 
-/*! \brief Clear any custom baudrate
+/*! Clear any custom baudrate
  *  \param[in] fd File descriptor of the open device
  *  \returns 0 for success or negative errno.
  *