add libasound2-dev in dependencies checking

configure.ac

@@ -163,6 +163,12 @@ dnl PKG_CHECK_MODULES(gsm, gsm >= ${LIBGSM1_MIN_VERSION})
 dnl SFLPHONE_CFLAGS="$SFLPHONE_CFLAGS $libgsm1_CFLAGS"
 dnl SFLPHONE_LIBS="$SFLPHONE_LIBS $libgsm1_LIBS"
 
+LIBASOUND2_MIN_VERSION=1.0
+PKG_CHECK_MODULES(alsa, alsa >= ${LIBASOUND2_MIN_VERSION})
+SFLPHONE_CFLAGS="$SFLPHONE_CFLAGS $libasound2_CFLAGS"
+SFLPHONE_LIBS="$SFLPHONE_LIBS $libasound2_LIBS"
+
+
 LIBSAMPLERATE_MIN_VERSION=0.1.1
 PKG_CHECK_MODULES(samplerate, samplerate >= ${LIBSAMPLERATE_MIN_VERSION})
 SFLPHONE_CFLAGS="$SFLPHONE_CFLAGS $samplerate_CFLAGS"