Set language=grammar for \lstinline grammar rule

chapters/functions.tex

@@ -1712,8 +1712,9 @@ \section{External Function Interface}\label{external-function-interface}
 This is just as for any other function.  The components in the protected part allow local variables for temporary storage to be declared.
 \end{nonnormative}
 
-The \lstinline!language-specification! must currently be one of \lstinline!"builtin"! (deprecated), \lstinline!"C"!, \lstinline!"C..."! (for one of the specific C standards like C89, C99, and C11 -- specifying
-that it relies on the C standard library of that version) or \lstinline!"FORTRAN 77"!.  Unless the external language is specified, it is assumed to be \lstinline!"C"!.
+The \lstinline[language=grammar]!language-specification! must currently be one of \lstinline!"builtin"! (deprecated), \lstinline!"C"!, \lstinline!"C..."! (for one of the specific C standards like C89, C99, and C11 -- specifying
+that it relies on the C standard library of that version) or \lstinline!"FORTRAN 77"!.
+Unless the external language is specified, it is assumed to be \lstinline!"C"!.
 
 \begin{nonnormative}
 The intended use of e.g.\ C99 is to detect if the user tries to link with a C99-function using a C89 compiler.