net: add m_max_inbound to connman

Extract the logic for calculating & maintaining inbound connection limits to be
a member within connman for consistency with other maximum connection limits.

Note that we now limit m_max_inbound to 0 and don't call
AttemptToEvictConnection() when we don't have any inbounds.
Previously, nMaxInbound could become negative if the user ran with a low
-maxconnections, which didn't break any logic but didn't make sense.

Co-authored-by: Martin Zumsande <mzumsande@gmail.com>

Author: amitiuttarwar

src/net.cpp

@@ -1777,7 +1777,6 @@ void CConnman::CreateNodeFromAcceptedSocket(std::unique_ptr<Sock>&& sock,
                                             const CAddress& addr)
 {
     int nInbound = 0;
-    int nMaxInbound = nMaxConnections - m_max_outbound;
 
     AddWhitelistPermissionFlags(permission_flags, addr);
     if (NetPermissions::HasFlag(permission_flags, NetPermissionFlags::Implicit)) {
@@ -1823,13 +1822,13 @@ void CConnman::CreateNodeFromAcceptedSocket(std::unique_ptr<Sock>&& sock,
 
     // Only accept connections from discouraged peers if our inbound slots aren't (almost) full.
     bool discouraged = m_banman && m_banman->IsDiscouraged(addr);
-    if (!NetPermissions::HasFlag(permission_flags, NetPermissionFlags::NoBan) && nInbound + 1 >= nMaxInbound && discouraged)
+    if (!NetPermissions::HasFlag(permission_flags, NetPermissionFlags::NoBan) && nInbound + 1 >= m_max_inbound && discouraged)
     {
         LogPrint(BCLog::NET, "connection from %s dropped (discouraged)\n", addr.ToStringAddrPort());
         return;
     }
 
-    if (nInbound >= nMaxInbound)
+    if (nInbound >= m_max_inbound)
     {
         if (!AttemptToEvictConnection()) {
             // No connection to evict, disconnect the new connection

src/net.h

@@ -1088,6 +1088,7 @@ class CConnman
         m_max_outbound_full_relay = std::min(MAX_OUTBOUND_FULL_RELAY_CONNECTIONS, nMaxConnections);
         m_max_outbound_block_relay = std::min(MAX_BLOCK_RELAY_ONLY_CONNECTIONS, nMaxConnections - m_max_outbound_full_relay);
         m_max_outbound = m_max_outbound_full_relay + m_max_outbound_block_relay + nMaxFeeler;
+        m_max_inbound = std::max(0, nMaxConnections - m_max_outbound);
         m_use_addrman_outgoing = connOptions.m_use_addrman_outgoing;
         m_client_interface = connOptions.uiInterface;
         m_banman = connOptions.m_banman;
@@ -1485,6 +1486,7 @@ class CConnman
     int nMaxAddnode{MAX_ADDNODE_CONNECTIONS};
     int nMaxFeeler{MAX_FEELER_CONNECTIONS};
     int m_max_outbound;
+    int m_max_inbound;
     bool m_use_addrman_outgoing;
     CClientUIInterface* m_client_interface;
     NetEventsInterface* m_msgproc;