contrib: update OpenDHT to 1.7.0rc7

Change-Id: If33e9f3bd89012e7c492b454edf3dec83a97c09c

contrib/src/opendht/SHA512SUMS

-a69c1879a7d78a60a3b0aca762d7b344619775c657590567904aa4076824ec453fee77fd0ff58c074748a01f937b314bd4041e098bf841a5108cfe7382537d42  opendht-1.7.0rc6.tar.gz
+8d19902de5f65617aa101b6391e04c716241f42d710566dcaa1863921d859a673b05a8b565bdb42a78e8018db2551dc0f05882b513e6ace07e6730d5a93164a2  opendht-1.7.0rc7.tar.gz

contrib/src/opendht/rules.mak

 # OPENDHT
-OPENDHT_VERSION := 1.7.0rc6
+OPENDHT_VERSION := 1.7.0rc7
 OPENDHT_URL := https://github.com/savoirfairelinux/opendht/archive/$(OPENDHT_VERSION).tar.gz
 
 PKGS += opendht