swr: add a swr_flags AVOption

Using swr_flags instead of plain flags will avoid conflicts that
arise with plain flags and multiple libs (which all have AVOption flags)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswresample/swresample.c

@@ -52,6 +52,7 @@ static const AVOption options[]={
 {"slev", "sourround mix level"  , OFFSET(slev)         , AV_OPT_TYPE_FLOAT, {.dbl=C_30DB}, 0, 4, 0},
 {"rmvol", "rematrix volume"     , OFFSET(rematrix_volume), AV_OPT_TYPE_FLOAT, {.dbl=1.0}, -1000, 1000, 0},
 {"flags", NULL                  , OFFSET(flags)        , AV_OPT_TYPE_FLAGS, {.dbl=0}, 0,  UINT_MAX, 0, "flags"},
+{"swr_flags", NULL              , OFFSET(flags)        , AV_OPT_TYPE_FLAGS, {.dbl=0}, 0,  UINT_MAX, 0, "flags"},
 {"res", "force resampling", 0, AV_OPT_TYPE_CONST, {.dbl=SWR_FLAG_RESAMPLE}, INT_MIN, INT_MAX, 0, "flags"},
 {"dither_scale" , "dither scale"       , OFFSET(dither_scale ), AV_OPT_TYPE_FLOAT, {.dbl=1}, 0, INT_MAX, 0},
 {"dither_method", "dither method"      , OFFSET(dither_method), AV_OPT_TYPE_INT  , {.dbl=0}, 0, SWR_DITHER_NB-1, 0, "dither_method"},