comgt-ncm: Add support for specifying profile index

Add support for specifying a call profile index instead of APN. A
specific index different from 1 must be used for some service
provider and modem combinations.

In addition, change the manufacturer detection to use the standard
AT+CGMI command, which produces more predictable output than ATI,
remove the redundant ipv6 option, since it is less ambiguous to
directly specify the PDP context type with mobile connections, and
fix missing device during teardown when using ncm through the wwan
proto.

Signed-off-by: Matti Laakso <malaakso@elisanet.fi>