Allow the characters .-+/ to appear in ppp profile names by folding them

to _ when evaluating ppp_<profile>_nat and ppp_<profile>_mode.  Document
the per-profile variables.

PR:		conf/121452, conf/122127 (partial)
MFC after:	1 week

etc/rc.d/ppp

@@ -21,17 +21,22 @@ ppp_start_profile()
 	local _ppp_profile _ppp_mode _ppp_nat
 
 	_ppp_profile=$1
+	_ppp_profile_cleaned=$1
+	_punct=". - / +"
+	for _punct_c in $_punct; do
+		_ppp_profile_cleaned=`ltr ${_ppp_profile_cleaned} ${_punct_c} '_'`
+	done
 
 	# Check for ppp profile mode override.
 	#
-	eval _ppp_mode=\$ppp_${_ppp_profile}_mode
+	eval _ppp_mode=\$ppp_${_ppp_profile_cleaned}_mode
 	if [ -z "$_ppp_mode" ]; then
 		_ppp_mode=$ppp_mode
 	fi
 
 	# Check for ppp profile nat override.
 	#
-	eval _ppp_nat=\$ppp_${_ppp_profile}_nat
+	eval _ppp_nat=\$ppp_${_ppp_profile_cleaned}_nat
 	if [ -z "$_ppp_nat" ]; then
 		_ppp_nat=$ppp_nat
 	fi

share/man/man5/rc.conf.5

@@ -1315,11 +1315,30 @@ If set to
 run the
 .Xr ppp 8
 daemon.
+.It Va ppp_profile
+.Pq Vt str
+The name of the profile to use from
+.Pa /etc/ppp/ppp.conf .
+Also used for per-profile overrides of
+.Va ppp_mode
+and
+.Va ppp_nat .
+When the profile name contains any of the characters
+.Dq Li .-/+
+they are translated to
+.Dq Li _
+for the proposes of the override variable names.
 .It Va ppp_mode
 .Pq Vt str
 Mode in which to run the
 .Xr ppp 8
 daemon.
+.It Va ppp_ Ns Ao Ar profile Ac Ns _mode
+.Pq Vt str
+Overrides the global
+.Va ppp_mode
+for
+.Ar profile .
 Accepted modes are
 .Dq Li auto ,
 .Dq Li ddial ,
@@ -1336,10 +1355,12 @@ Used in conjunction with
 .Va gateway_enable
 allows hosts on private network addresses access to the Internet using
 this host as a network address translating router.
-.It Va ppp_profile
+.It Va ppp_ Ns Ao Ar profile Ac Ns _nat
 .Pq Vt str
-The name of the profile to use from
-.Pa /etc/ppp/ppp.conf .
+Overrides the global
+.Va ppp_nat
+for
+.Ar profile .
 .It Va ppp_user
 .Pq Vt str
 The name of the user under which