gr-ofdm: update to a40720c7 (20180306).

science/gr-ofdm/Portfile

@@ -6,11 +6,11 @@ PortGroup           github 1.0
 PortGroup           active_variants 1.1
 PortGroup           cxx11 1.1
 
-github.setup        rwth-ti gr-ofdm 8c0f81c38a67439df9f2d7b03d5cf31cb4e8d859
-version             20170823
-revision            5
-checksums           rmd160 d3fec2c94ad038c4ac333e21a398a1978e5ff932 \
-                    sha256 450928a83a9c5f4bdb8159fa59d8037cdc08973ff580c8979bdbf90c0eef2587
+github.setup        rwth-ti gr-ofdm a40720c708b75ad4c12ff09e49931879e9f90e78
+version             20180306
+checksums           rmd160 ee1f3054e00e57986fa7536d9691018c69e9e68a \
+                    sha256 b053745b3590f1842a35c9914b344db295c2a479ce65711cc3112dc848427e7b \
+                    size   3257234
 
 # allow gr-ofdm to work with both gnuradio and gnuradio-devel ...