gprs_gmm.c: Call mmctx_set_(p)mm_state only on related ran_type
For new readers it's very confusing why PMM states and MM states are in
the same enum, but handled with different functions, and sometimes
called one right after the other with different enums. Calling them when
on a different ran_type makes the function early return, so let's better
conditionally call the function to make it clear in the flow when the
function is expected to do something.
Change-Id: I65ad9e180177bc9fc7c4a037cd85cfe33b161f73