Fixed the incorrect APN dedupling

Fixed that APN settings can't be merged when one APN
entry has MTU set, but the other doesn't. Also default
MTU unset value to 0 for backwards compatability.

Test: atest DataProfileManagerTest & Manual testing
Fix: 226563054
Change-Id: Ibf84657aa76d52c46ee45890a1af2c940553acd4
1 file changed