adding space modulation frequency offset test

kat_test/random/space_mod_f_offset.kat

+# test to ensure space phase modulation is happening correctly for frequency offsets
+# and in both directions
+
+l i1 1 1000 n0
+s s1 1000000 n0 n3
+l i2 1 1000 n3
+
+fsig sig1 s1 1u 0	
+
+ad a1 1000.000001 n3
+ad a2 999.999999 n3
+ad a3 1000.000001 n0
+ad a4 999.999999 n0
+
+noxaxis
+yaxis deg
+
+gnuterm no