Answer is 8. As per Table B.1-1 of 36.331 following DRB combinations are supported, based on featureGroupIndicators, received in UE capability information message .
Case 1 ( Bit 7 and bit 20 are set 1 ) :
SRB1 and SRB2 for DCCH + 8x AM DRB OR SRB1 and SRB2 for DCCH + 5x AM DRB + 3x UM DRB
Case 2 ( BIT 7 is set 0 and BIT 20 is set to 1) :
SRB1 and SRB2 for DCCH + 8x AM DRB
Case 3 ( BIT 7 and BIT 20 are set to any value ie 0/1) :
SRB1 and SRB2 for DCCH + 4x AM DRB
Case 4 ( BIT 7 is set to 1 and BIT 20 is set to any value 0/1) :
SRB1 and SRB2 for DCCH + 4x AM DRB + 1 UM DRB
I hope this should clarify ur doubt.