codec_builtin: Use multiples of 20 for maximum_ms

Allows the test to accept maxptime as a variable value.
Some providers require a multiple of 20 for the maxptime or fail to complete calls,
e.g. Vivo in Brazil. To increase compatibility, only multiples of 20 are now used.

Resolves: #15

tests/channels/pjsip/sdp_offer_answer/incoming/nominal/single-media-stream/audio/packetization/sipp/uac-ptime-accept.xml

@@ -53,7 +53,7 @@
       <ereg regexp="a=ptime:30+..*"
             search_in="body" check_it="true" assign_to="2"/>
       <test assign_to="2" variable="2" compare="equal" value=""/>
-      <ereg regexp="a=maxptime:150+..*"
+      <ereg regexp="a=maxptime:140+..*"
             search_in="body" check_it="true" assign_to="3"/>
       <test assign_to="3" variable="3" compare="equal" value=""/>
     </action>

tests/channels/pjsip/sdp_offer_answer/incoming/nominal/single-media-stream/audio/packetization/sipp/uac-ptime-decline-endpoint.xml

@@ -53,7 +53,7 @@
       <ereg regexp="a=ptime:40+..*"
             search_in="body" check_it="true" assign_to="2"/>
       <test assign_to="2" variable="2" compare="equal" value=""/>
-      <ereg regexp="a=maxptime:150+..*"
+      <ereg regexp="a=maxptime:140+..*"
             search_in="body" check_it="true" assign_to="3"/>
       <test assign_to="3" variable="3" compare="equal" value=""/>
     </action>

tests/channels/pjsip/sdp_offer_answer/incoming/nominal/single-media-stream/audio/packetization/sipp/uac-ptime-endpoint.xml

@@ -52,7 +52,7 @@
       <ereg regexp="a=ptime:40+..*"
             search_in="body" check_it="true" assign_to="2"/>
       <test assign_to="2" variable="2" compare="equal" value=""/>
-      <ereg regexp="a=maxptime:150+..*"
+      <ereg regexp="a=maxptime:140+..*"
             search_in="body" check_it="true" assign_to="3"/>
       <test assign_to="3" variable="3" compare="equal" value=""/>
     </action>