Add new argument for mac_ctx in definition of tx_timer_create macro
so that its caller can use any local variable name for mac context.
Currently pMac is hardcoded as first param in definition of the macro
which prohibits caller of that function from using any other name.
Change-Id: Id901424ba16846eab62c00a80d48a5c85c73bea6
CRs-Fixed: 824222
a20cd9f91d