Fixes setting of service uuid mask during BLE APCF scan

Fixes setting of incorrect service uuid mask bytes in vendor
specific command when service uuid mask length is less than
the length of service uuid APCF filter.
eg:ServiceUuid:12131215-0000-1000-8000-00805F9B34FB
SvcMaskUuid:0000FFFF-0000-1000-8000-00805F9B34FB
In the above eg, user is trying to apply 32 bit service uuid
mask on 32 bit service uuid. But the stack treats the
service uuid mask as 16 bits and inserts garbage values for
the first 16 bits of service uuid mask in the VS command
since the MSB bits of the mask are zeroes. This change fixes
the scenario where service uuid mask length is less than
service uuid length.

Change-Id: Ie1aece1162b1ba7f4b7a3e9eea7eb5a074f85d62