net/remmina: force libsoup2

If libsoup3 is present in the system, remmina might pick it even if it is
expected to use libsoup2. This results in an error like:

libsoup-ERROR **: 09:36:19.231: libsoup3 symbols detected. Using libsoup2 and
libsoup3 in the same process is not supported.

Force libsoup2.

PR:             271557
Reported by:    root@dc365.ru