LeAudio: Fix LTV vector creation macros

If we pass int to UINT16_TO_VEC_UINT8, we expect the output vector to be
2 octets long, with 2 LS bytes from 4 bytes long integer type, while the
existing macro was generating 4 octets, thus it worked just like
UINT32_TO_VEC_UINT8.

We have these macros named explicitly with types, to make the type
conversion happen. It is important for the LTV packed structures, since
Bluetooth spec. clearly defines LTV field lengths for the specified field types.

Bug: 7813203315
Test: atest bluetooth_le_audio_test
Change-Id: I2e19e6695f6e09237d3a3573cddbef403d9cfd50