Parse the server host name field of the dhcp package

Some hotspot devices will fill in the server host name field of the DHCP
package, such as iphone. Parsing the server host name of the DHCP
package can help identify ios hotspots.

Bug: 120584519
Test: 127423755
Test: builds, boots, wifi works
Change-Id: I8c5a7dc8ab117f062f9401f58832edada321436b
Merged-In: I60071bc029d25485bf204cfd3a8cebd538ca12b6
(cherry picked from commit 43f1bc9d)