umbim: use IP configuration provided by MBIM by default

umbim: use IP configuration provided by MBIM by default

Previously, DHCP was used. According to MBIM Specification v1.0 errata 1 [1],
section 10.5.20, MBIM_CID_IP_CONFIGURATION,
if MBIM information element containing IP configuration is available,
host shall use it, and fall back to in-band mechanisms to acquire it therwise -
therefore make static configuration the default.

[1] https://www.usb.org/document-library/mobile-broadband-interface-model-v10-errata-1-and-adopters-agreement

Signed-off-by: Lech Perczak <lech.perczak@gmail.com>