patch 8.2.1597: the channel source file is too big

Problem:    The channel source file is too big.
Solution:   Move job related code to a new source file.
diff --git a/src/configure.ac b/src/configure.ac
index 6176dc9..d262990 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -2143,9 +2143,9 @@
 fi
 if test "$enable_channel" = "yes"; then
   AC_DEFINE(FEAT_JOB_CHANNEL)
-  CHANNEL_SRC="channel.c"
+  CHANNEL_SRC="job.c channel.c"
   AC_SUBST(CHANNEL_SRC)
-  CHANNEL_OBJ="objects/channel.o"
+  CHANNEL_OBJ="objects/job.o objects/channel.o"
   AC_SUBST(CHANNEL_OBJ)
 fi