doc: Set chunk.first.sections in XSLT, for consistency with DSSSL output

doc/src/sgml/stylesheet.xsl

@@ -17,6 +17,7 @@
 <xsl:param name="generate.legalnotice.link" select="1"></xsl:param>
 <xsl:param name="link.mailto.url">pgsql-docs@postgresql.org</xsl:param>
 <xsl:param name="chunker.output.indent" select="'yes'"/>
+<xsl:param name="chunk.first.sections" select="1"/>
 <xsl:param name="chunk.quietly" select="1"></xsl:param>
 <xsl:param name="toc.max.depth">2</xsl:param>