Improve modem help section

[MMaiero]

The modem help section should be improved to give to users a more accurate description on what PDP contexts to use in relation to the modem and wireless provider.

For example, we could update it with the following:

LTE Modems
* LE910C1-EU => ATD*99***4#
* LE910-EU1 and LE910EU-V2 => ATD*99***2# or ATD*99***1# (modem power cycle required)
* LE910NA-V2 with Verizon Wireless => ATD*99***3#
* Other modems or mobile network operators => please consult the documentation of the modem manufacturer and the mobile network operator

[cdealti]

LTE Modems
* LE910C1-EU => ATD*99***4#
* LE910C1-AP (Telstra) => ATD*99***1# or ATD*99***5#
* LE910-EU1 and LE910EU-V2 => ATD*99***2# or ATD*99***1# (modem power cycle required)
* LE910EU-V2 => ATD*99***2#
* LE910NA-V2 (AT&T) => ATD*99***1#
* LE910NA-V2 (Verizon Wireless) => ATD*99***3#
* Other modems or mobile network operators => please consult the documentation of the modem manufacturer and the mobile network operator

[MMaiero]

Changes performed