Fix two problems in CSubNet parsing

Fix two CSubNet constructor problems:

- The use of `/x` where 8 does not divide x was broken, due to a
  bit-order issue

- The use of e.g. `1.2.3.4/24` where the netmasked bits in the network
  are not 0 was broken. Fix this by explicitly normalizing the netwok
  according to the bitmask.

Also add tests for these cases.

Fixes #6179. Thanks to @jonasschnelli for reporting and initial fix.

src/netbase.cpp

@@ -1260,7 +1260,7 @@ CSubNet::CSubNet(const std::string &strSubnet, bool fAllowLookup)
                     n += astartofs*8;
                     // Clear bits [n..127]
                     for (; n < 128; ++n)
-                        netmask[n>>3] &= ~(1<<(n&7));
+                        netmask[n>>3] &= ~(1<<(7-(n&7)));
                 }
                 else
                 {
@@ -1287,6 +1287,10 @@ CSubNet::CSubNet(const std::string &strSubnet, bool fAllowLookup)
     {
         valid = false;
     }
+
+    // Normalize network according to netmask
+    for(int x=0; x<16; ++x)
+        network.ip[x] &= netmask[x];
 }
 
 bool CSubNet::Match(const CNetAddr &addr) const

src/test/netbase_tests.cpp

@@ -117,6 +117,11 @@ BOOST_AUTO_TEST_CASE(subnet_test)
     BOOST_CHECK(CSubNet("1:2:3:4:5:6:7:8").Match(CNetAddr("1:2:3:4:5:6:7:8")));
     BOOST_CHECK(!CSubNet("1:2:3:4:5:6:7:8").Match(CNetAddr("1:2:3:4:5:6:7:9")));
     BOOST_CHECK(CSubNet("1:2:3:4:5:6:7:0/112").Match(CNetAddr("1:2:3:4:5:6:7:1234")));
+    BOOST_CHECK(CSubNet("192.168.0.1/24").Match(CNetAddr("192.168.0.2")));
+    BOOST_CHECK(CSubNet("192.168.0.20/29").Match(CNetAddr("192.168.0.18")));
+    BOOST_CHECK(CSubNet("1.2.2.1/24").Match(CNetAddr("1.2.2.4")));
+    BOOST_CHECK(CSubNet("1.2.2.110/31").Match(CNetAddr("1.2.2.111")));
+    BOOST_CHECK(CSubNet("1.2.2.20/26").Match(CNetAddr("1.2.2.63")));
     // All-Matching IPv6 Matches arbitrary IPv4 and IPv6
     BOOST_CHECK(CSubNet("::/0").Match(CNetAddr("1:2:3:4:5:6:7:1234")));
     BOOST_CHECK(CSubNet("::/0").Match(CNetAddr("1.2.3.4")));