x11-toolkits/libshumate: switch to libsoup2 for shortwave

$ shortwave
(<unknown>:1234): libsoup-ERROR **: libsoup3 symbols detected. Using libsoup2 and libsoup3 in the same process is not supported.
Trace/BPT trap

$ pkg info -xr soup
gstreamer1-plugins-soup-1.16.2_2:

shortwave-3.1.0

libsoup-2.74.3:

gstreamer1-plugins-soup-1.16.2_2

libsoup3-3.2.1:

libshumate-1.0.0.b