Don't set media state to active when SDP contain "a=inactive" attribute

[trengginas]

SDP may specify a=inactive with media port set to non zero.

v=0
o=- 3872230549 3872230550 IN IP4 192.168.1.121
s=pjmedia
b=AS:84
t=0 0
a=X-nat:0
m=audio 4002 RTP/AVP 0 120
c=IN IP4 192.168.1.121
b=TIAS:64000
a=rtcp:4003 IN IP4 192.168.1.121
a=rtpmap:0 PCMU/8000
a=rtpmap:120 telephone-event/8000
a=fmtp:120 0-16
a=ssrc:2705443 cname:39b32d12074d4dc8
a=inactive

Currently, the library will set the media state to PJSUA_CALL_MEDIA_ACTIVE. It should set the media state to PJSUA_CALL_MEDIA_NONE same as when media port is set to 0.