channel.c: Fix NewCallerid AMI event not been sent on Caller ID change

channel.c: Fix NewCallerid AMI event not been sent on Caller ID change

Currently, NewCallerid is sent only when pointers to number or name
strings change, which is not always the case. The newly allocated string
may use the same memory, so pointers match, while the content
is different. As a result, Caller ID updates are often not reported.

With this patch, actual strings are compared, not the pointers.

ASTERISK-25427 #close
Reported by: Ivan Poddubny

Change-Id: I2a1ac3a842f0e092c6058d1cd3e35443bece1b36