[net][sal] Add SAL (socket abstraction layer) framework

components/net/sal_socket/SConscript

@@ -0,0 +1,31 @@
+# RT-Thread building script for component
+
+from building import *
+
+cwd = GetCurrentDir()
+
+src = Glob('src/*.c')
+src += Glob('socket/*.c')
+
+CPPPATH = [cwd + '/include']
+CPPPATH += [cwd + '/include/dfs_net']
+CPPPATH += [cwd + '/include/socket']
+
+if GetDepend('SAL_USING_LWIP'):
+    src += Glob('impl/af_inet_lwip.c')
+
+if GetDepend('SAL_USING_AT'):
+    src += Glob('impl/af_inet_at.c')
+
+if GetDepend('SAL_USING_POSIX'):
+    src += Glob('dfs_net/*.c')
+    
+    if not GetDepend('HAVE_SYS_SELECT_H'):
+        CPPPATH += [cwd + '/include/dfs_net/sys_select']
+
+    if not GetDepend('HAVE_SYS_SOCKET_H'):
+        CPPPATH += [cwd + '/include/socket/sys_socket']
+
+group = DefineGroup('SAL', src, depend = ['RT_USING_SAL'], CPPPATH = CPPPATH)
+
+Return('group')