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/include/osmocom/core/gsmtap.h b/include/osmocom/core/gsmtap.h
index f9d6f0a..0dc25bb 100644
--- a/include/osmocom/core/gsmtap.h
+++ b/include/osmocom/core/gsmtap.h
@@ -238,7 +238,7 @@
 };
 
 /* ====== DO NOT MAKE UNAPPROVED MODIFICATIONS HERE ===== */
-/*! \brief Structure of the GTMTAP pseudo-header */
+/*! Structure of the GTMTAP pseudo-header */
 struct gsmtap_hdr {
 	uint8_t version;	/*!< version, set to 0x01 currently */
 	uint8_t hdr_len;	/*!< length in number of 32bit words */
@@ -258,7 +258,7 @@
 
 } __attribute__((packed));
 
-/*! \brief Structure of the GTMTAP libosmocore logging header */
+/*! Structure of the GTMTAP libosmocore logging header */
 struct gsmtap_osmocore_log_hdr {
 	struct {
 		uint32_t sec;