Fix GCC 9.1 build warnings

GCC wants operator= aand copy ctor to be both defined, or neither

contrib/epee/include/net/net_utils_base.h

@@ -294,6 +294,11 @@ namespace net_utils
                                m_max_speed_up(0)
     {}
 
+    connection_context_base(const connection_context_base& a): connection_context_base()
+    {
+      set_details(a.m_connection_id, a.m_remote_address, a.m_is_income, a.m_ssl);
+    }
+
     connection_context_base& operator=(const connection_context_base& a)
     {
       set_details(a.m_connection_id, a.m_remote_address, a.m_is_income, a.m_ssl);

src/device/device_ledger.cpp

@@ -90,6 +90,20 @@ namespace hw {
       AKout = keys.AKout;
     }
 
+    ABPkeys &ABPkeys::operator=(const ABPkeys& keys) {
+      if (&keys == this)
+        return *this;
+      Aout = keys.Aout;
+      Bout = keys.Bout;
+      is_subaddress = keys.is_subaddress;
+      is_change_address = keys.is_change_address;
+      additional_key = keys.additional_key;
+      index = keys.index;
+      Pout = keys.Pout;
+      AKout = keys.AKout;
+      return *this;
+    }
+
     bool Keymap::find(const rct::key& P, ABPkeys& keys) const {
       size_t sz = ABP.size();
       for (size_t i=0; i<sz; i++) {

src/device/device_ledger.hpp

@@ -77,6 +77,7 @@ namespace hw {
         ABPkeys(const rct::key& A, const rct::key& B, const bool is_subaddr, bool is_subaddress, bool is_change_address, size_t index, const rct::key& P,const rct::key& AK);
         ABPkeys(const ABPkeys& keys) ;
         ABPkeys() {index=0;is_subaddress=false;is_subaddress=false;is_change_address=false;}
+        ABPkeys &operator=(const ABPkeys &keys);
     };
 
     class Keymap {