Use isMobileDataCapable helper in NetworkAndInternet

Disabling telephony support may be done either with the
config_show_sim_info config option, or based on whether
TelephonyManager reports data capabilities. The isMobileDataCapable()
helper method ensures both ways are supported.

With this change, if config_show_sim_info=false, the "Network and
Internet" page menu entry won't make any reference to "Mobile", in the
same way as if FEATURE_TELEPHONY_DATA is not set.

Bug: 395714454
Test: mm && atest
Flag: EXEMPT bugfix
Change-Id: I223b5c0c5f04a45f899b4d22a578a262d93108ad