"Unfix" the filter length calculation
"Unfix" the filter length calculation

Partially reverts 3f3a3ac4f1d069542ca2399a8b5e63d9d1a4df3b. The l*2 + 1 is
correct when you want an odd number of sample points, which avoids an
unnecessary phase offset in the fitler. However, the rounding is still needed
to calculating the left offset (l), or else the transition width can increase
with an odd-numbered order.

aaronmjacobs/openal-soft,aaronmjacobs/openal-soft