Add net/if header documentation and update CMake configuration and include it in index

Author: StarOne01

libc/docs/CMakeLists.txt

@@ -19,6 +19,7 @@ if (SPHINX_FOUND)
     file(MAKE_DIRECTORY
       "${CMAKE_CURRENT_BINARY_DIR}/headers/arpa/"
       "${CMAKE_CURRENT_BINARY_DIR}/headers/sys/"
+      "${CMAKE_CURRENT_BINARY_DIR}/headers/net/"
     )
 
     # Change sphinx to build from $build_dir/libc/docs/ rather than
@@ -40,6 +41,7 @@ if (SPHINX_FOUND)
       float
       inttypes
       locale
+      net/if
       setjmp
       signal
       stdbit

libc/docs/headers/index.rst

@@ -14,6 +14,7 @@ Implementation Status
    inttypes
    locale
    math/index.rst
+   net/if
    search
    setjmp
    signal

libc/utils/docgen/net/if.yaml

@@ -0,0 +1,13 @@
+functions:
+  if_freenameindex:
+    in-latest-posix: ''
+  if_indextoname:
+    in-latest-posix: ''
+  if_nameindex:
+    in-latest-posix: ''
+  if_nametoindex:
+    in-latest-posix: ''
+
+macros:
+  IF_NAMESIZE:
+    in-latest-posix: ''