SG_MUL_VAL_ need to be grouped using message id as well

[bmcpt]

If the following file is parsed using dbcppp, the New_Signal_4 multiplexer value will be applied to signal of New_Message_4 as well, even though it's message id doesn't match.

VERSION ""

NS_ :
	NS_DESC_
	CM_
	BA_DEF_
	BA_
	VAL_
	CAT_DEF_
	CAT_
	FILTER
	BA_DEF_DEF_
	EV_DATA_
	ENVVAR_DATA_
	SGTYPE_
	SGTYPE_VAL_
	BA_DEF_SGTYPE_
	BA_SGTYPE_
	SIG_TYPE_REF_
	VAL_TABLE_
	SIG_GROUP_
	SIG_VALTYPE_
	SIGTYPE_VALTYPE_
	BO_TX_BU_
	BA_DEF_REL_
	BA_REL_
	BA_DEF_DEF_REL_
	BU_SG_REL_
	BU_EV_REL_
	BU_BO_REL_
	SG_MUL_VAL_

BS_:

BU_:


BO_ 2348873389 New_Message_1: 1024 Vector__XXX
 SG_ New_Signal_4 m0 : 32|8@1- (1,0) [0|0] "" Vector__XXX
 SG_ New_Signal_3 : 48|8@1- (1,0) [0|0] "" Vector__XXX
 SG_ New_Signal_2 m0M : 24|8@1- (1,0) [0|0] "" Vector__XXX
 SG_ New_Signal_1 M : 0|24@1- (1,0) [0|0] "" Vector__XXX

BO_ 2348941054 New_Message_4: 8 Vector__XXX
 SG_ New_Signal_4 : 0|8@1- (1,0) [0|0] "" Vector__XXX


SG_MUL_VAL_ 2348873389 New_Signal_4 New_Signal_2 0-0;
SG_MUL_VAL_ 2348873389 New_Signal_2 New_Signal_1 1-1, 2-1, 5-7;