Update the Virgin Mobile UK MMS APN definition

This corrects the MMS settings to match those seen on Virgin provided stock handsets and
fixes receiving of media messages.
MNCs 31 and 32 are likely to also require changing but have not been tested so are
unchanged by this patch.

Change-Id: I6bc40fa7bfa7f21cf3c6a36cdef2b46512075c6a
Signed-off-by: Pat Thoyts <patthoyts@gmail.com>