NetworkInterface does not support get_mac_address()

### Description
- Type: Bug
- Priority: Major

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## Bug

**Target**
K64F

**Toolchain:**
GCC_ARM|ARM|IAR

**meed-os sha:**
latest release/master

Currently I cannot call get_mac_address() with NetworkInterface class. This could be fixed by adding:

 virtual const char *get_mac_address() = 0;

to features/net/network-socket/NetworkInterface.h

Could this be added there?
