Kernel: Respond to packets sent to the directed broadcast address

The last IP address in an IPv4 subnet is considered the directed
broadcast address, e.g. for 192.168.3.0/24 the directed broadcast
address is 192.168.3.255. We need to consider this address as
belonging to the interface.

Here's an example with this fix applied, SerenityOS has 192.168.3.190:

[gunnar@nyx ~]$ ping -b 192.168.3.255
WARNING: pinging broadcast address
PING 192.168.3.255 (192.168.3.255) 56(84) bytes of data.
64 bytes from 192.168.3.175: icmp_seq=1 ttl=64 time=0.950 ms
64 bytes from 192.168.3.188: icmp_seq=1 ttl=64 time=2.33 ms
64 bytes from 192.168.3.46: icmp_seq=1 ttl=64 time=2.77 ms
64 bytes from 192.168.3.41: icmp_seq=1 ttl=64 time=4.15 ms
64 bytes from 192.168.3.190: icmp_seq=1 ttl=64 time=29.4 ms
64 bytes from 192.168.3.42: icmp_seq=1 ttl=64 time=30.8 ms
64 bytes from 192.168.3.55: icmp_seq=1 ttl=64 time=31.0 ms
64 bytes from 192.168.3.30: icmp_seq=1 ttl=64 time=33.2 ms
64 bytes from 192.168.3.31: icmp_seq=1 ttl=64 time=33.2 ms
64 bytes from 192.168.3.173: icmp_seq=1 ttl=64 time=41.7 ms
64 bytes from 192.168.3.43: icmp_seq=1 ttl=64 time=47.7 ms
^C
--- 192.168.3.255 ping statistics ---
1 packets transmitted, 1 received, +10 duplicates, 0% packet loss,
time 0ms, rtt min/avg/max/mdev = 0.950/23.376/47.676/16.539 ms
[gunnar@nyx ~]$

Kernel/Net/NetworkAdapter.cpp

@@ -37,7 +37,7 @@ RefPtr<NetworkAdapter> NetworkAdapter::from_ipv4_address(const IPv4Address& addr
 {
     Locker locker(all_adapters().lock());
     for (auto* adapter : all_adapters().resource()) {
-        if (adapter->ipv4_address() == address)
+        if (adapter->ipv4_address() == address || adapter->ipv4_broadcast() == address)
             return adapter;
     }
     if (address[0] == 127)

Kernel/Net/NetworkAdapter.h

@@ -36,6 +36,7 @@ public:
     MACAddress mac_address() { return m_mac_address; }
     IPv4Address ipv4_address() const { return m_ipv4_address; }
     IPv4Address ipv4_netmask() const { return m_ipv4_netmask; }
+    IPv4Address ipv4_broadcast() const { return IPv4Address { (m_ipv4_address.to_u32() & m_ipv4_netmask.to_u32()) | ~m_ipv4_netmask.to_u32() }; }
     IPv4Address ipv4_gateway() const { return m_ipv4_gateway; }
     virtual bool link_up() { return false; }