nimble/ll: Fix PHY transition on LL_PHY_UPDATE_IND
nimble/ll: Fix PHY transition on LL_PHY_UPDATE_IND

s_to_m_phy field is a PHY bitmask, not a PHY number, so we need to
decode it properly as otherwise during transition to LE Coded we'll fail
to adjust TX payload length (1M and 2M work only because bitmask is the
same as number).

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble